From 49b2fd6ea63d7fe9c81f00e6d0117827db1d30c6 Mon Sep 17 00:00:00 2001 From: Jonathan Cameron Date: Sun, 1 Jan 2017 12:32:45 +0000 Subject: docs: IIO documentation sphinx conversion This is a manual conversion of the existing DocBook documentation for IIO. The intent is not to substantially change any of the content in this patch, but to give a base to build upon. Signed-off-by: Jonathan Cameron Signed-off-by: Jonathan Corbet --- Documentation/DocBook/Makefile | 2 +- Documentation/DocBook/iio.tmpl | 697 --------------------- Documentation/driver-api/iio/buffers.rst | 125 ++++ Documentation/driver-api/iio/core.rst | 182 ++++++ Documentation/driver-api/iio/index.rst | 17 + Documentation/driver-api/iio/intro.rst | 33 + Documentation/driver-api/iio/triggered-buffers.rst | 69 ++ Documentation/driver-api/iio/triggers.rst | 80 +++ Documentation/driver-api/index.rst | 1 + 9 files changed, 508 insertions(+), 698 deletions(-) delete mode 100644 Documentation/DocBook/iio.tmpl create mode 100644 Documentation/driver-api/iio/buffers.rst create mode 100644 Documentation/driver-api/iio/core.rst create mode 100644 Documentation/driver-api/iio/index.rst create mode 100644 Documentation/driver-api/iio/intro.rst create mode 100644 Documentation/driver-api/iio/triggered-buffers.rst create mode 100644 Documentation/driver-api/iio/triggers.rst (limited to 'Documentation') diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index a6eb7dcd4dd5..c95b1aa47b45 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -13,7 +13,7 @@ DOCBOOKS := z8530book.xml \ gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \ sh.xml regulator.xml w1.xml \ - writing_musb_glue_layer.xml iio.xml + writing_musb_glue_layer.xml ifeq ($(DOCBOOKS),) diff --git a/Documentation/DocBook/iio.tmpl b/Documentation/DocBook/iio.tmpl deleted file mode 100644 index e2ab6a1f223e..000000000000 --- a/Documentation/DocBook/iio.tmpl +++ /dev/null @@ -1,697 +0,0 @@ - - - - - - Industrial I/O driver developer's guide - - - - Daniel - Baluta - -
- daniel.baluta@intel.com -
- - - - - - 2015 - Intel Corporation - - - - - This documentation is free software; you can redistribute - it and/or modify it under the terms of the GNU General Public - License version 2. - - - - - - - - Introduction - - The main purpose of the Industrial I/O subsystem (IIO) is to provide - support for devices that in some sense perform either analog-to-digital - conversion (ADC) or digital-to-analog conversion (DAC) or both. The aim - is to fill the gap between the somewhat similar hwmon and input - subsystems. - Hwmon is directed at low sample rate sensors used to monitor and - control the system itself, like fan speed control or temperature - measurement. Input is, as its name suggests, focused on human interaction - input devices (keyboard, mouse, touchscreen). In some cases there is - considerable overlap between these and IIO. - - - Devices that fall into this category include: - - - analog to digital converters (ADCs) - - - accelerometers - - - capacitance to digital converters (CDCs) - - - digital to analog converters (DACs) - - - gyroscopes - - - inertial measurement units (IMUs) - - - color and light sensors - - - magnetometers - - - pressure sensors - - - proximity sensors - - - temperature sensors - - - Usually these sensors are connected via SPI or I2C. A common use case of the - sensors devices is to have combined functionality (e.g. light plus proximity - sensor). - - - - Industrial I/O core - - The Industrial I/O core offers: - - - a unified framework for writing drivers for many different types of - embedded sensors. - - - a standard interface to user space applications manipulating sensors. - - - The implementation can be found under - drivers/iio/industrialio-* - - - Industrial I/O devices - -!Finclude/linux/iio/iio.h iio_dev -!Fdrivers/iio/industrialio-core.c iio_device_alloc -!Fdrivers/iio/industrialio-core.c iio_device_free -!Fdrivers/iio/industrialio-core.c iio_device_register -!Fdrivers/iio/industrialio-core.c iio_device_unregister - - - An IIO device usually corresponds to a single hardware sensor and it - provides all the information needed by a driver handling a device. - Let's first have a look at the functionality embedded in an IIO - device then we will show how a device driver makes use of an IIO - device. - - - There are two ways for a user space application to interact - with an IIO driver. - - - /sys/bus/iio/iio:deviceX/, this - represents a hardware sensor and groups together the data - channels of the same chip. - - - /dev/iio:deviceX, character device node - interface used for buffered data transfer and for events information - retrieval. - - - - A typical IIO driver will register itself as an I2C or SPI driver and will - create two routines, probe and remove - . At probe: - - call iio_device_alloc, which allocates memory - for an IIO device. - - initialize IIO device fields with driver specific information - (e.g. device name, device channels). - - call iio_device_register, this registers the - device with the IIO core. After this call the device is ready to accept - requests from user space applications. - - - At remove, we free the resources allocated in - probe in reverse order: - - iio_device_unregister, unregister the device - from the IIO core. - - iio_device_free, free the memory allocated - for the IIO device. - - - - IIO device sysfs interface - - Attributes are sysfs files used to expose chip info and also allowing - applications to set various configuration parameters. For device - with index X, attributes can be found under - /sys/bus/iio/iio:deviceX/ directory. - Common attributes are: - - name, description of the physical - chip. - - dev, shows the major:minor pair - associated with /dev/iio:deviceX node. - - sampling_frequency_available, - available discrete set of sampling frequency values for - device. - - - Available standard attributes for IIO devices are described in the - Documentation/ABI/testing/sysfs-bus-iio file - in the Linux kernel sources. - - - IIO device channels -!Finclude/linux/iio/iio.h iio_chan_spec structure. - - An IIO device channel is a representation of a data channel. An - IIO device can have one or multiple channels. For example: - - - a thermometer sensor has one channel representing the - temperature measurement. - - - a light sensor with two channels indicating the measurements in - the visible and infrared spectrum. - - - an accelerometer can have up to 3 channels representing - acceleration on X, Y and Z axes. - - - An IIO channel is described by the struct iio_chan_spec - . A thermometer driver for the temperature sensor in the - example above would have to describe its channel as follows: - - static const struct iio_chan_spec temp_channel[] = { - { - .type = IIO_TEMP, - .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), - }, - }; - - - Channel sysfs attributes exposed to userspace are specified in - the form of bitmasks. Depending on their - shared info, attributes can be set in one of the following masks: - - info_mask_separate, attributes will - be specific to this channel - info_mask_shared_by_type, - attributes are shared by all channels of the same type - info_mask_shared_by_dir, attributes - are shared by all channels of the same direction - info_mask_shared_by_all, - attributes are shared by all channels - - When there are multiple data channels per channel type we have two - ways to distinguish between them: - - set .modified field of - iio_chan_spec to 1. Modifiers are specified using - .channel2 field of the same - iio_chan_spec structure and are used to indicate a - physically unique characteristic of the channel such as its direction - or spectral response. For example, a light sensor can have two channels, - one for infrared light and one for both infrared and visible light. - - set .indexed field of - iio_chan_spec to 1. In this case the channel is - simply another instance with an index specified by the - .channel field. - - - Here is how we can make use of the channel's modifiers: - - static const struct iio_chan_spec light_channels[] = { - { - .type = IIO_INTENSITY, - .modified = 1, - .channel2 = IIO_MOD_LIGHT_IR, - .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), - .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), - }, - { - .type = IIO_INTENSITY, - .modified = 1, - .channel2 = IIO_MOD_LIGHT_BOTH, - .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), - .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), - }, - { - .type = IIO_LIGHT, - .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), - .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), - }, - - } - - This channel's definition will generate two separate sysfs files - for raw data retrieval: - - - /sys/bus/iio/iio:deviceX/in_intensity_ir_raw - - - /sys/bus/iio/iio:deviceX/in_intensity_both_raw - - - one file for processed data: - - - /sys/bus/iio/iio:deviceX/in_illuminance_input - - - - and one shared sysfs file for sampling frequency: - - - /sys/bus/iio/iio:deviceX/sampling_frequency. - - - - - - Here is how we can make use of the channel's indexing: - - static const struct iio_chan_spec light_channels[] = { - { - .type = IIO_VOLTAGE, - .indexed = 1, - .channel = 0, - .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), - }, - { - .type = IIO_VOLTAGE, - .indexed = 1, - .channel = 1, - .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), - }, - } - - This will generate two separate attributes files for raw data - retrieval: - - - /sys/bus/iio/devices/iio:deviceX/in_voltage0_raw, - representing voltage measurement for channel 0. - - - /sys/bus/iio/devices/iio:deviceX/in_voltage1_raw, - representing voltage measurement for channel 1. - - - - - - - Industrial I/O buffers -!Finclude/linux/iio/buffer.h iio_buffer -!Edrivers/iio/industrialio-buffer.c - - - The Industrial I/O core offers a way for continuous data capture - based on a trigger source. Multiple data channels can be read at once - from /dev/iio:deviceX character device node, - thus reducing the CPU load. - - - - IIO buffer sysfs interface - - An IIO buffer has an associated attributes directory under - /sys/bus/iio/iio:deviceX/buffer/. Here are the existing - attributes: - - - length, the total number of data samples - (capacity) that can be stored by the buffer. - - - enable, activate buffer capture. - - - - - - IIO buffer setup - The meta information associated with a channel reading - placed in a buffer is called a scan element . - The important bits configuring scan elements are exposed to - userspace applications via the - /sys/bus/iio/iio:deviceX/scan_elements/ directory. This - file contains attributes of the following form: - - enable, used for enabling a channel. - If and only if its attribute is non zero, then a triggered capture - will contain data samples for this channel. - - type, description of the scan element - data storage within the buffer and hence the form in which it is - read from user space. Format is - [be|le]:[s|u]bits/storagebitsXrepeat[>>shift] . - - be or le, specifies - big or little endian. - - - s or u, specifies if - signed (2's complement) or unsigned. - - bits, is the number of valid data - bits. - - storagebits, is the number of bits - (after padding) that it occupies in the buffer. - - - shift, if specified, is the shift that needs - to be applied prior to masking out unused bits. - - - repeat, specifies the number of bits/storagebits - repetitions. When the repeat element is 0 or 1, then the repeat - value is omitted. - - - - - For example, a driver for a 3-axis accelerometer with 12 bit - resolution where data is stored in two 8-bits registers as - follows: - - 7 6 5 4 3 2 1 0 - +---+---+---+---+---+---+---+---+ - |D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06) - +---+---+---+---+---+---+---+---+ - - 7 6 5 4 3 2 1 0 - +---+---+---+---+---+---+---+---+ - |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07) - +---+---+---+---+---+---+---+---+ - - - will have the following scan element type for each axis: - - $ cat /sys/bus/iio/devices/iio:device0/scan_elements/in_accel_y_type - le:s12/16>>4 - - A user space application will interpret data samples read from the - buffer as two byte little endian signed data, that needs a 4 bits - right shift before masking out the 12 valid bits of data. - - - For implementing buffer support a driver should initialize the following - fields in iio_chan_spec definition: - - struct iio_chan_spec { - /* other members */ - int scan_index - struct { - char sign; - u8 realbits; - u8 storagebits; - u8 shift; - u8 repeat; - enum iio_endian endianness; - } scan_type; - }; - - The driver implementing the accelerometer described above will - have the following channel definition: - - struct struct iio_chan_spec accel_channels[] = { - { - .type = IIO_ACCEL, - .modified = 1, - .channel2 = IIO_MOD_X, - /* other stuff here */ - .scan_index = 0, - .scan_type = { - .sign = 's', - .realbits = 12, - .storagebits = 16, - .shift = 4, - .endianness = IIO_LE, - }, - } - /* similar for Y (with channel2 = IIO_MOD_Y, scan_index = 1) - * and Z (with channel2 = IIO_MOD_Z, scan_index = 2) axis - */ - } - - - - Here scan_index defines the order in which - the enabled channels are placed inside the buffer. Channels with a lower - scan_index will be placed before channels with a higher index. Each - channel needs to have a unique scan_index. - - - Setting scan_index to -1 can be used to indicate that the specific - channel does not support buffered capture. In this case no entries will - be created for the channel in the scan_elements directory. - - - - - Industrial I/O triggers -!Finclude/linux/iio/trigger.h iio_trigger -!Edrivers/iio/industrialio-trigger.c - - In many situations it is useful for a driver to be able to - capture data based on some external event (trigger) as opposed - to periodically polling for data. An IIO trigger can be provided - by a device driver that also has an IIO device based on hardware - generated events (e.g. data ready or threshold exceeded) or - provided by a separate driver from an independent interrupt - source (e.g. GPIO line connected to some external system, timer - interrupt or user space writing a specific file in sysfs). A - trigger may initiate data capture for a number of sensors and - also it may be completely unrelated to the sensor itself. - - - IIO trigger sysfs interface - There are two locations in sysfs related to triggers: - - /sys/bus/iio/devices/triggerY, - this file is created once an IIO trigger is registered with - the IIO core and corresponds to trigger with index Y. Because - triggers can be very different depending on type there are few - standard attributes that we can describe here: - - - name, trigger name that can be later - used for association with a device. - - - sampling_frequency, some timer based - triggers use this attribute to specify the frequency for - trigger calls. - - - - - /sys/bus/iio/devices/iio:deviceX/trigger/, this - directory is created once the device supports a triggered - buffer. We can associate a trigger with our device by writing - the trigger's name in the current_trigger file. - - - - - IIO trigger setup - - - Let's see a simple example of how to setup a trigger to be used - by a driver. - - - struct iio_trigger_ops trigger_ops = { - .set_trigger_state = sample_trigger_state, - .validate_device = sample_validate_device, - } - - struct iio_trigger *trig; - - /* first, allocate memory for our trigger */ - trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx); - - /* setup trigger operations field */ - trig->ops = &trigger_ops; - - /* now register the trigger with the IIO core */ - iio_trigger_register(trig); - - - - - IIO trigger ops -!Finclude/linux/iio/trigger.h iio_trigger_ops - - Notice that a trigger has a set of operations attached: - - - set_trigger_state, switch the trigger on/off - on demand. - - - validate_device, function to validate the - device when the current trigger gets changed. - - - - - - - Industrial I/O triggered buffers - - Now that we know what buffers and triggers are let's see how they - work together. - - IIO triggered buffer setup -!Edrivers/iio/buffer/industrialio-triggered-buffer.c -!Finclude/linux/iio/iio.h iio_buffer_setup_ops - - - - A typical triggered buffer setup looks like this: - - const struct iio_buffer_setup_ops sensor_buffer_setup_ops = { - .preenable = sensor_buffer_preenable, - .postenable = sensor_buffer_postenable, - .postdisable = sensor_buffer_postdisable, - .predisable = sensor_buffer_predisable, - }; - - irqreturn_t sensor_iio_pollfunc(int irq, void *p) - { - pf->timestamp = iio_get_time_ns((struct indio_dev *)p); - return IRQ_WAKE_THREAD; - } - - irqreturn_t sensor_trigger_handler(int irq, void *p) - { - u16 buf[8]; - int i = 0; - - /* read data for each active channel */ - for_each_set_bit(bit, active_scan_mask, masklength) - buf[i++] = sensor_get_data(bit) - - iio_push_to_buffers_with_timestamp(indio_dev, buf, timestamp); - - iio_trigger_notify_done(trigger); - return IRQ_HANDLED; - } - - /* setup triggered buffer, usually in probe function */ - iio_triggered_buffer_setup(indio_dev, sensor_iio_polfunc, - sensor_trigger_handler, - sensor_buffer_setup_ops); - - - The important things to notice here are: - - iio_buffer_setup_ops, the buffer setup - functions to be called at predefined points in the buffer configuration - sequence (e.g. before enable, after disable). If not specified, the - IIO core uses the default iio_triggered_buffer_setup_ops. - - sensor_iio_pollfunc, the function that - will be used as top half of poll function. It should do as little - processing as possible, because it runs in interrupt context. The most - common operation is recording of the current timestamp and for this reason - one can use the IIO core defined iio_pollfunc_store_time - function. - - sensor_trigger_handler, the function that - will be used as bottom half of the poll function. This runs in the - context of a kernel thread and all the processing takes place here. - It usually reads data from the device and stores it in the internal - buffer together with the timestamp recorded in the top half. - - - - - - - Resources - IIO core may change during time so the best documentation to read is the - source code. There are several locations where you should look: - - - drivers/iio/, contains the IIO core plus - and directories for each sensor type (e.g. accel, magnetometer, - etc.) - - - include/linux/iio/, contains the header - files, nice to read for the internal kernel interfaces. - - - include/uapi/linux/iio/, contains files to be - used by user space applications. - - - tools/iio/, contains tools for rapidly - testing buffers, events and device creation. - - - drivers/staging/iio/, contains code for some - drivers or experimental features that are not yet mature enough - to be moved out. - - - - Besides the code, there are some good online documentation sources: - - - Industrial I/O mailing - list - - - - Analog Device IIO wiki page - - - - Using the Linux IIO framework for SDR, Lars-Peter Clausen's - presentation at FOSDEM - - - - - - - diff --git a/Documentation/driver-api/iio/buffers.rst b/Documentation/driver-api/iio/buffers.rst new file mode 100644 index 000000000000..02c99a6bee18 --- /dev/null +++ b/Documentation/driver-api/iio/buffers.rst @@ -0,0 +1,125 @@ +======= +Buffers +======= + +* struct :c:type:`iio_buffer` — general buffer structure +* :c:func:`iio_validate_scan_mask_onehot` — Validates that exactly one channel + is selected +* :c:func:`iio_buffer_get` — Grab a reference to the buffer +* :c:func:`iio_buffer_put` — Release the reference to the buffer + +The Industrial I/O core offers a way for continuous data capture based on a +trigger source. Multiple data channels can be read at once from +:file:`/dev/iio:device{X}` character device node, thus reducing the CPU load. + +IIO buffer sysfs interface +========================== +An IIO buffer has an associated attributes directory under +:file:`/sys/bus/iio/iio:device{X}/buffer/*`. Here are some of the existing +attributes: + +* :file:`length`, the total number of data samples (capacity) that can be + stored by the buffer. +* :file:`enable`, activate buffer capture. + +IIO buffer setup +================ + +The meta information associated with a channel reading placed in a buffer is +called a scan element . The important bits configuring scan elements are +exposed to userspace applications via the +:file:`/sys/bus/iio/iio:device{X}/scan_elements/*` directory. This file contains +attributes of the following form: + +* :file:`enable`, used for enabling a channel. If and only if its attribute + is non *zero*, then a triggered capture will contain data samples for this + channel. +* :file:`type`, description of the scan element data storage within the buffer + and hence the form in which it is read from user space. + Format is [be|le]:[s|u]bits/storagebitsXrepeat[>>shift] . + * *be* or *le*, specifies big or little endian. + * *s* or *u*, specifies if signed (2's complement) or unsigned. + * *bits*, is the number of valid data bits. + * *storagebits*, is the number of bits (after padding) that it occupies in the + buffer. + * *shift*, if specified, is the shift that needs to be applied prior to + masking out unused bits. + * *repeat*, specifies the number of bits/storagebits repetitions. When the + repeat element is 0 or 1, then the repeat value is omitted. + +For example, a driver for a 3-axis accelerometer with 12 bit resolution where +data is stored in two 8-bits registers as follows:: + + 7 6 5 4 3 2 1 0 + +---+---+---+---+---+---+---+---+ + |D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06) + +---+---+---+---+---+---+---+---+ + + 7 6 5 4 3 2 1 0 + +---+---+---+---+---+---+---+---+ + |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07) + +---+---+---+---+---+---+---+---+ + +will have the following scan element type for each axis:: + + $ cat /sys/bus/iio/devices/iio:device0/scan_elements/in_accel_y_type + le:s12/16>>4 + +A user space application will interpret data samples read from the buffer as +two byte little endian signed data, that needs a 4 bits right shift before +masking out the 12 valid bits of data. + +For implementing buffer support a driver should initialize the following +fields in iio_chan_spec definition:: + + struct iio_chan_spec { + /* other members */ + int scan_index + struct { + char sign; + u8 realbits; + u8 storagebits; + u8 shift; + u8 repeat; + enum iio_endian endianness; + } scan_type; + }; + +The driver implementing the accelerometer described above will have the +following channel definition:: + + struct struct iio_chan_spec accel_channels[] = { + { + .type = IIO_ACCEL, + .modified = 1, + .channel2 = IIO_MOD_X, + /* other stuff here */ + .scan_index = 0, + .scan_type = { + .sign = 's', + .realbits = 12, + .storagebits = 16, + .shift = 4, + .endianness = IIO_LE, + }, + } + /* similar for Y (with channel2 = IIO_MOD_Y, scan_index = 1) + * and Z (with channel2 = IIO_MOD_Z, scan_index = 2) axis + */ + } + +Here **scan_index** defines the order in which the enabled channels are placed +inside the buffer. Channels with a lower **scan_index** will be placed before +channels with a higher index. Each channel needs to have a unique +**scan_index**. + +Setting **scan_index** to -1 can be used to indicate that the specific channel +does not support buffered capture. In this case no entries will be created for +the channel in the scan_elements directory. + +More details +============ +.. kernel-doc:: include/linux/iio/buffer.h +.. kernel-doc:: drivers/iio/industrialio-buffer.c + :export: + diff --git a/Documentation/driver-api/iio/core.rst b/Documentation/driver-api/iio/core.rst new file mode 100644 index 000000000000..9a34ae03b679 --- /dev/null +++ b/Documentation/driver-api/iio/core.rst @@ -0,0 +1,182 @@ +============= +Core elements +============= + +The Industrial I/O core offers a unified framework for writing drivers for +many different types of embedded sensors. a standard interface to user space +applications manipulating sensors. The implementation can be found under +:file:`drivers/iio/industrialio-*` + +Industrial I/O Devices +---------------------- + +* struct :c:type:`iio_dev` - industrial I/O device +* :c:func:`iio_device_alloc()` - alocate an :c:type:`iio_dev` from a driver +* :c:func:`iio_device_free()` - free an :c:type:`iio_dev` from a driver +* :c:func:`iio_device_register()` - register a device with the IIO subsystem +* :c:func:`iio_device_unregister()` - unregister a device from the IIO + subsystem + +An IIO device usually corresponds to a single hardware sensor and it +provides all the information needed by a driver handling a device. +Let's first have a look at the functionality embedded in an IIO device +then we will show how a device driver makes use of an IIO device. + +There are two ways for a user space application to interact with an IIO driver. + +1. :file:`/sys/bus/iio/iio:device{X}/`, this represents a hardware sensor + and groups together the data channels of the same chip. +2. :file:`/dev/iio:device{X}`, character device node interface used for + buffered data transfer and for events information retrieval. + +A typical IIO driver will register itself as an :doc:`I2C <../i2c>` or +:doc:`SPI <../spi>` driver and will create two routines, probe and remove. + +At probe: + +1. Call :c:func:`iio_device_alloc()`, which allocates memory for an IIO device. +2. Initialize IIO device fields with driver specific information (e.g. + device name, device channels). +3. Call :c:func:`iio_device_register()`, this registers the device with the + IIO core. After this call the device is ready to accept requests from user + space applications. + +At remove, we free the resources allocated in probe in reverse order: + +1. :c:func:`iio_device_unregister()`, unregister the device from the IIO core. +2. :c:func:`iio_device_free()`, free the memory allocated for the IIO device. + +IIO device sysfs interface +========================== + +Attributes are sysfs files used to expose chip info and also allowing +applications to set various configuration parameters. For device with +index X, attributes can be found under /sys/bus/iio/iio:deviceX/ directory. +Common attributes are: + +* :file:`name`, description of the physical chip. +* :file:`dev`, shows the major:minor pair associated with + :file:`/dev/iio:deviceX` node. +* :file:`sampling_frequency_available`, available discrete set of sampling + frequency values for device. +* Available standard attributes for IIO devices are described in the + :file:`Documentation/ABI/testing/sysfs-bus-iio` file in the Linux kernel + sources. + +IIO device channels +=================== + +struct :c:type:`iio_chan_spec` - specification of a single channel + +An IIO device channel is a representation of a data channel. An IIO device can +have one or multiple channels. For example: + +* a thermometer sensor has one channel representing the temperature measurement. +* a light sensor with two channels indicating the measurements in the visible + and infrared spectrum. +* an accelerometer can have up to 3 channels representing acceleration on X, Y + and Z axes. + +An IIO channel is described by the struct :c:type:`iio_chan_spec`. +A thermometer driver for the temperature sensor in the example above would +have to describe its channel as follows:: + + static const struct iio_chan_spec temp_channel[] = { + { + .type = IIO_TEMP, + .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), + }, + }; + +Channel sysfs attributes exposed to userspace are specified in the form of +bitmasks. Depending on their shared info, attributes can be set in one of the +following masks: + +* **info_mask_separate**, attributes will be specific to + this channel +* **info_mask_shared_by_type**, attributes are shared by all channels of the + same type +* **info_mask_shared_by_dir**, attributes are shared by all channels of the same + direction +* **info_mask_shared_by_all**, attributes are shared by all channels + +When there are multiple data channels per channel type we have two ways to +distinguish between them: + +* set **.modified** field of :c:type:`iio_chan_spec` to 1. Modifiers are + specified using **.channel2** field of the same :c:type:`iio_chan_spec` + structure and are used to indicate a physically unique characteristic of the + channel such as its direction or spectral response. For example, a light + sensor can have two channels, one for infrared light and one for both + infrared and visible light. +* set **.indexed** field of :c:type:`iio_chan_spec` to 1. In this case the + channel is simply another instance with an index specified by the **.channel** + field. + +Here is how we can make use of the channel's modifiers:: + + static const struct iio_chan_spec light_channels[] = { + { + .type = IIO_INTENSITY, + .modified = 1, + .channel2 = IIO_MOD_LIGHT_IR, + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), + .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), + }, + { + .type = IIO_INTENSITY, + .modified = 1, + .channel2 = IIO_MOD_LIGHT_BOTH, + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), + .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), + }, + { + .type = IIO_LIGHT, + .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), + .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), + }, + } + +This channel's definition will generate two separate sysfs files for raw data +retrieval: + +* :file:`/sys/bus/iio/iio:device{X}/in_intensity_ir_raw` +* :file:`/sys/bus/iio/iio:device{X}/in_intensity_both_raw` + +one file for processed data: + +* :file:`/sys/bus/iio/iio:device{X}/in_illuminance_input` + +and one shared sysfs file for sampling frequency: + +* :file:`/sys/bus/iio/iio:device{X}/sampling_frequency`. + +Here is how we can make use of the channel's indexing:: + + static const struct iio_chan_spec light_channels[] = { + { + .type = IIO_VOLTAGE, + .indexed = 1, + .channel = 0, + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), + }, + { + .type = IIO_VOLTAGE, + .indexed = 1, + .channel = 1, + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), + }, + } + +This will generate two separate attributes files for raw data retrieval: + +* :file:`/sys/bus/iio/devices/iio:device{X}/in_voltage0_raw`, representing + voltage measurement for channel 0. +* :file:`/sys/bus/iio/devices/iio:device{X}/in_voltage1_raw`, representing + voltage measurement for channel 1. + +More details +============ +.. kernel-doc:: include/linux/iio/iio.h +.. kernel-doc:: drivers/iio/industrialio-core.c + :export: diff --git a/Documentation/driver-api/iio/index.rst b/Documentation/driver-api/iio/index.rst new file mode 100644 index 000000000000..e5c3922d1b6f --- /dev/null +++ b/Documentation/driver-api/iio/index.rst @@ -0,0 +1,17 @@ +.. include:: + +Industrial I/O +============== + +**Copyright** |copy| 2015 Intel Corporation + +Contents: + +.. toctree:: + :maxdepth: 2 + + intro + core + buffers + triggers + triggered-buffers diff --git a/Documentation/driver-api/iio/intro.rst b/Documentation/driver-api/iio/intro.rst new file mode 100644 index 000000000000..3653fbd57069 --- /dev/null +++ b/Documentation/driver-api/iio/intro.rst @@ -0,0 +1,33 @@ +.. include:: + +============ +Introduction +============ + +The main purpose of the Industrial I/O subsystem (IIO) is to provide support +for devices that in some sense perform either +analog-to-digital conversion (ADC) or digital-to-analog conversion (DAC) +or both. The aim is to fill the gap between the somewhat similar hwmon and +:doc:`input <../input>` subsystems. Hwmon is directed at low sample rate +sensors used to monitor and control the system itself, like fan speed control +or temperature measurement. :doc:`Input <../input>` is, as its name suggests, +focused on human interaction input devices (keyboard, mouse, touchscreen). +In some cases there is considerable overlap between these and IIO. + +Devices that fall into this category include: + +* analog to digital converters (ADCs) +* accelerometers +* capacitance to digital converters (CDCs) +* digital to analog converters (DACs) +* gyroscopes +* inertial measurement units (IMUs) +* color and light sensors +* magnetometers +* pressure sensors +* proximity sensors +* temperature sensors + +Usually these sensors are connected via :doc:`SPI <../spi>` or +:doc:`I2C <../i2c>`. A common use case of the sensors devices is to have +combined functionality (e.g. light plus proximity sensor). diff --git a/Documentation/driver-api/iio/triggered-buffers.rst b/Documentation/driver-api/iio/triggered-buffers.rst new file mode 100644 index 000000000000..0db12660cc90 --- /dev/null +++ b/Documentation/driver-api/iio/triggered-buffers.rst @@ -0,0 +1,69 @@ +================= +Triggered Buffers +================= + +Now that we know what buffers and triggers are let's see how they work together. + +IIO triggered buffer setup +========================== + +* :c:func:`iio_triggered_buffer_setup` — Setup triggered buffer and pollfunc +* :c:func:`iio_triggered_buffer_cleanup` — Free resources allocated by + :c:func:`iio_triggered_buffer_setup` +* struct :c:type:`iio_buffer_setup_ops` — buffer setup related callbacks + +A typical triggered buffer setup looks like this:: + + const struct iio_buffer_setup_ops sensor_buffer_setup_ops = { + .preenable = sensor_buffer_preenable, + .postenable = sensor_buffer_postenable, + .postdisable = sensor_buffer_postdisable, + .predisable = sensor_buffer_predisable, + }; + + irqreturn_t sensor_iio_pollfunc(int irq, void *p) + { + pf->timestamp = iio_get_time_ns((struct indio_dev *)p); + return IRQ_WAKE_THREAD; + } + + irqreturn_t sensor_trigger_handler(int irq, void *p) + { + u16 buf[8]; + int i = 0; + + /* read data for each active channel */ + for_each_set_bit(bit, active_scan_mask, masklength) + buf[i++] = sensor_get_data(bit) + + iio_push_to_buffers_with_timestamp(indio_dev, buf, timestamp); + + iio_trigger_notify_done(trigger); + return IRQ_HANDLED; + } + + /* setup triggered buffer, usually in probe function */ + iio_triggered_buffer_setup(indio_dev, sensor_iio_polfunc, + sensor_trigger_handler, + sensor_buffer_setup_ops); + +The important things to notice here are: + +* :c:type:`iio_buffer_setup_ops`, the buffer setup functions to be called at + predefined points in the buffer configuration sequence (e.g. before enable, + after disable). If not specified, the IIO core uses the default + iio_triggered_buffer_setup_ops. +* **sensor_iio_pollfunc**, the function that will be used as top half of poll + function. It should do as little processing as possible, because it runs in + interrupt context. The most common operation is recording of the current + timestamp and for this reason one can use the IIO core defined + :c:func:`iio_pollfunc_store_time` function. +* **sensor_trigger_handler**, the function that will be used as bottom half of + the poll function. This runs in the context of a kernel thread and all the + processing takes place here. It usually reads data from the device and + stores it in the internal buffer together with the timestamp recorded in the + top half. + +More details +============ +.. kernel-doc:: drivers/iio/buffer/industrialio-triggered-buffer.c diff --git a/Documentation/driver-api/iio/triggers.rst b/Documentation/driver-api/iio/triggers.rst new file mode 100644 index 000000000000..f89d37e7dd82 --- /dev/null +++ b/Documentation/driver-api/iio/triggers.rst @@ -0,0 +1,80 @@ +======== +Triggers +======== + +* struct :c:type:`iio_trigger` — industrial I/O trigger device +* :c:func:`devm_iio_trigger_alloc` — Resource-managed iio_trigger_alloc +* :c:func:`devm_iio_trigger_free` — Resource-managed iio_trigger_free +* :c:func:`devm_iio_trigger_register` — Resource-managed iio_trigger_register +* :c:func:`devm_iio_trigger_unregister` — Resource-managed + iio_trigger_unregister +* :c:func:`iio_trigger_validate_own_device` — Check if a trigger and IIO + device belong to the same device + +In many situations it is useful for a driver to be able to capture data based +on some external event (trigger) as opposed to periodically polling for data. +An IIO trigger can be provided by a device driver that also has an IIO device +based on hardware generated events (e.g. data ready or threshold exceeded) or +provided by a separate driver from an independent interrupt source (e.g. GPIO +line connected to some external system, timer interrupt or user space writing +a specific file in sysfs). A trigger may initiate data capture for a number of +sensors and also it may be completely unrelated to the sensor itself. + +IIO trigger sysfs interface +=========================== + +There are two locations in sysfs related to triggers: + +* :file:`/sys/bus/iio/devices/trigger{Y}/*`, this file is created once an + IIO trigger is registered with the IIO core and corresponds to trigger + with index Y. + Because triggers can be very different depending on type there are few + standard attributes that we can describe here: + + * :file:`name`, trigger name that can be later used for association with a + device. + * :file:`sampling_frequency`, some timer based triggers use this attribute to + specify the frequency for trigger calls. + +* :file:`/sys/bus/iio/devices/iio:device{X}/trigger/*`, this directory is + created once the device supports a triggered buffer. We can associate a + trigger with our device by writing the trigger's name in the + :file:`current_trigger` file. + +IIO trigger setup +================= + +Let's see a simple example of how to setup a trigger to be used by a driver:: + + struct iio_trigger_ops trigger_ops = { + .set_trigger_state = sample_trigger_state, + .validate_device = sample_validate_device, + } + + struct iio_trigger *trig; + + /* first, allocate memory for our trigger */ + trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx); + + /* setup trigger operations field */ + trig->ops = &trigger_ops; + + /* now register the trigger with the IIO core */ + iio_trigger_register(trig); + +IIO trigger ops +=============== + +* struct :c:type:`iio_trigger_ops` — operations structure for an iio_trigger. + +Notice that a trigger has a set of operations attached: + +* :file:`set_trigger_state`, switch the trigger on/off on demand. +* :file:`validate_device`, function to validate the device when the current + trigger gets changed. + +More details +============ +.. kernel-doc:: include/linux/iio/trigger.h +.. kernel-doc:: drivers/iio/industrialio-trigger.c + :export: diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index 5475a2807e7a..a2e5db07756c 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -21,6 +21,7 @@ available subsections can be seen below. message-based sound frame-buffer + iio/index input usb spi -- cgit v1.2.3 From 843e4d1ed9e5c4a5d7e42adf0a2ab078f8978946 Mon Sep 17 00:00:00 2001 From: Shilpasri G Bhat Date: Fri, 16 Dec 2016 16:47:42 +0530 Subject: Note that the POWER[89] processors are supported. Documentation: cpufreq: Update supported powernv processors Signed-off-by: Shilpasri G Bhat Acked-by: Viresh Kumar Signed-off-by: Jonathan Corbet --- Documentation/cpu-freq/user-guide.txt | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/cpu-freq/user-guide.txt b/Documentation/cpu-freq/user-guide.txt index 109e97bbab77..5e10d5f4d9b0 100644 --- a/Documentation/cpu-freq/user-guide.txt +++ b/Documentation/cpu-freq/user-guide.txt @@ -87,7 +87,9 @@ UltraSPARC-III ------- Several "PowerBook" and "iBook2" notebooks are supported. - +The following POWER processors are supported in powernv mode: +POWER8 +POWER9 1.5 SuperH ---------- -- cgit v1.2.3 From 0a4cbc53d7986967503c1fc6450110fbf1db3b4b Mon Sep 17 00:00:00 2001 From: Colin Ian King Date: Wed, 28 Dec 2016 21:51:37 +0000 Subject: Documentation: fix spelling mistakes of "Celcius" -- > "Celsius" Signed-off-by: Colin Ian King Acked-by: Guenter Roeck Signed-off-by: Jonathan Corbet --- Documentation/hwmon/ds1621 | 8 ++++---- Documentation/thermal/nouveau_thermal | 2 +- 2 files changed, 5 insertions(+), 5 deletions(-) (limited to 'Documentation') diff --git a/Documentation/hwmon/ds1621 b/Documentation/hwmon/ds1621 index f775e612f582..fa3407997795 100644 --- a/Documentation/hwmon/ds1621 +++ b/Documentation/hwmon/ds1621 @@ -117,10 +117,10 @@ support, which is achieved via the R0 and R1 config register bits, where: R0..R1 ------ - 0 0 => 9 bits, 0.5 degrees Celcius - 1 0 => 10 bits, 0.25 degrees Celcius - 0 1 => 11 bits, 0.125 degrees Celcius - 1 1 => 12 bits, 0.0625 degrees Celcius + 0 0 => 9 bits, 0.5 degrees Celsius + 1 0 => 10 bits, 0.25 degrees Celsius + 0 1 => 11 bits, 0.125 degrees Celsius + 1 1 => 12 bits, 0.0625 degrees Celsius Note: At initial device power-on, the default resolution is set to 12-bits. diff --git a/Documentation/thermal/nouveau_thermal b/Documentation/thermal/nouveau_thermal index 60bc29357ac3..6e17a11efcb0 100644 --- a/Documentation/thermal/nouveau_thermal +++ b/Documentation/thermal/nouveau_thermal @@ -42,7 +42,7 @@ thresholds can be configured thanks to the following HWMON attributes: * Critical: temp1_crit and temp1_crit_hyst; * Shutdown: temp1_emergency and temp1_emergency_hyst. -NOTE: Remember that the values are stored as milli degrees Celcius. Don't forget +NOTE: Remember that the values are stored as milli degrees Celsius. Don't forget to multiply! Fan management -- cgit v1.2.3 From e1235e18b502610becb99a1b6971a2afbbe02fa5 Mon Sep 17 00:00:00 2001 From: Sanjeev Date: Sat, 24 Dec 2016 16:27:29 +0800 Subject: Doc: Correct PPS doc to reflect code location timepps.h , as well as PPS sample test utilities, are no longer in the kernel tree. Update documentation to point to new locations. Signed-off-by: Sanjeev Gupta Signed-off-by: Jonathan Corbet --- Documentation/pps/pps.txt | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'Documentation') diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt index 50022b3c8ebf..a15a1169cbd9 100644 --- a/Documentation/pps/pps.txt +++ b/Documentation/pps/pps.txt @@ -166,7 +166,8 @@ Testing the PPS support In order to test the PPS support even without specific hardware you can use the ktimer driver (see the client subsection in the PPS configuration menu) -and the userland tools provided in the Documentation/pps/ directory. +and the userland tools available in your distribution's pps-tools package, +http://linuxpps.org , or https://github.com/ago/pps-tools . Once you have enabled the compilation of ktimer just modprobe it (if not statically compiled): @@ -183,8 +184,8 @@ and the run ppstest as follow: source 0 - assert 1186592700.388931295, sequence: 365 - clear 0.000000000, sequence: 0 source 0 - assert 1186592701.389032765, sequence: 366 - clear 0.000000000, sequence: 0 -Please, note that to compile userland programs you need the file timepps.h -(see Documentation/pps/). +Please, note that to compile userland programs you need the file timepps.h . +This is available in the pps-tools repository mentioned above. Generators -- cgit v1.2.3 From fe4c56c98c1338c0b8b69d08ccf5694bf8e1dcaf Mon Sep 17 00:00:00 2001 From: Sanjeev Date: Sat, 24 Dec 2016 16:27:30 +0800 Subject: Doc: Typos in documentation No semantic changes. The next patch in this series will do the actual changes to sync with NTP current best practices Signed-off-by: Sanjeev Gupta Signed-off-by: Jonathan Corbet --- Documentation/pps/pps.txt | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt index a15a1169cbd9..a9f53bba910d 100644 --- a/Documentation/pps/pps.txt +++ b/Documentation/pps/pps.txt @@ -63,7 +63,7 @@ for instance) is a PPS source too, and if not they should provide the possibility to open another device as PPS source. In LinuxPPS the PPS sources are simply char devices usually mapped -into files /dev/pps0, /dev/pps1, etc.. +into files /dev/pps0, /dev/pps1, etc. PPS with USB to serial devices @@ -71,7 +71,7 @@ PPS with USB to serial devices It is possible to grab the PPS from an USB to serial device. However, you should take into account the latencies and jitter introduced by -the USB stack. Users has reported clock instability around +-1ms when +the USB stack. Users have reported clock instability around +-1ms when synchronized with PPS through USB. This isn't suited for time server synchronization. -- cgit v1.2.3 From f2c1a053ceedec87aa355fafe60db1af27d7d830 Mon Sep 17 00:00:00 2001 From: Sanjeev Date: Sat, 24 Dec 2016 16:27:31 +0800 Subject: Doc: clarify source of jitter in USB1.1, and USB2.0 Even though the jitter due to USB1.1 may be 1ms, NTP can reduce its effect significantly. And USB2.0 reduces this anyway. Signed-off-by: Sanjeev Gupta Signed-off-by: Jonathan Corbet --- Documentation/pps/pps.txt | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt index a9f53bba910d..1fdbd5447216 100644 --- a/Documentation/pps/pps.txt +++ b/Documentation/pps/pps.txt @@ -72,8 +72,11 @@ PPS with USB to serial devices It is possible to grab the PPS from an USB to serial device. However, you should take into account the latencies and jitter introduced by the USB stack. Users have reported clock instability around +-1ms when -synchronized with PPS through USB. This isn't suited for time server -synchronization. +synchronized with PPS through USB. With USB 2.0, jitter may decrease +down to the order of 125 microseconds. + +This may be suitable for time server synchronization with NTP because +of its undersampling and algorithms. If your device doesn't report PPS, you can check that the feature is supported by its driver. Most of the time, you only need to add a call -- cgit v1.2.3 From ff58fa7f556c1d87061e4a91ed875d5f8aa9571f Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Thu, 22 Dec 2016 17:19:34 +0100 Subject: Documentation: Update CPU hotplug and move it to core-api The current CPU hotplug is outdated. During the update to what we currently have I rewrote it partly and moved to sphinx format. Cc: Jonathan Corbet Cc: Mauro Carvalho Chehab Cc: Rusty Russell Cc: Srivatsa Vaddagiri Cc: Ashok Raj Cc: Joel Schopp Cc: linux-doc@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Jonathan Corbet --- Documentation/core-api/cpu_hotplug.rst | 372 +++++++++++++++++++++++++++ Documentation/core-api/index.rst | 1 + Documentation/cpu-hotplug.txt | 452 --------------------------------- 3 files changed, 373 insertions(+), 452 deletions(-) create mode 100644 Documentation/core-api/cpu_hotplug.rst delete mode 100644 Documentation/cpu-hotplug.txt (limited to 'Documentation') diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst new file mode 100644 index 000000000000..4a50ab7817f7 --- /dev/null +++ b/Documentation/core-api/cpu_hotplug.rst @@ -0,0 +1,372 @@ +========================= +CPU hotplug in the Kernel +========================= + +:Date: December, 2016 +:Author: Sebastian Andrzej Siewior , + Rusty Russell , + Srivatsa Vaddagiri , + Ashok Raj , + Joel Schopp + +Introduction +============ + +Modern advances in system architectures have introduced advanced error +reporting and correction capabilities in processors. There are couple OEMS that +support NUMA hardware which are hot pluggable as well, where physical node +insertion and removal require support for CPU hotplug. + +Such advances require CPUs available to a kernel to be removed either for +provisioning reasons, or for RAS purposes to keep an offending CPU off +system execution path. Hence the need for CPU hotplug support in the +Linux kernel. + +A more novel use of CPU-hotplug support is its use today in suspend resume +support for SMP. Dual-core and HT support makes even a laptop run SMP kernels +which didn't support these methods. + + +Command Line Switches +===================== +``maxcpus=n`` + Restrict boot time CPUs to *n*. Say if you have fourV CPUs, using + ``maxcpus=2`` will only boot two. You can choose to bring the + other CPUs later online. + +``nr_cpus=n`` + Restrict the total amount CPUs the kernel will support. If the number + supplied here is lower than the number of physically available CPUs than + those CPUs can not be brought online later. + +``additional_cpus=n`` + Use this to limit hotpluggable CPUs. This option sets + ``cpu_possible_mask = cpu_present_mask + additional_cpus`` + + This option is limited to the IA64 architecture. + +``possible_cpus=n`` + This option sets ``possible_cpus`` bits in ``cpu_possible_mask``. + + This option is limited to the X86 and S390 architecture. + +``cede_offline={"off","on"}`` + Use this option to disable/enable putting offlined processors to an extended + ``H_CEDE`` state on supported pseries platforms. If nothing is specified, + ``cede_offline`` is set to "on". + + This option is limited to the PowerPC architecture. + +``cpu0_hotplug`` + Allow to shutdown CPU0. + + This option is limited to the X86 architecture. + +CPU maps +======== + +``cpu_possible_mask`` + Bitmap of possible CPUs that can ever be available in the + system. This is used to allocate some boot time memory for per_cpu variables + that aren't designed to grow/shrink as CPUs are made available or removed. + Once set during boot time discovery phase, the map is static, i.e no bits + are added or removed anytime. Trimming it accurately for your system needs + upfront can save some boot time memory. + +``cpu_online_mask`` + Bitmap of all CPUs currently online. Its set in ``__cpu_up()`` + after a CPU is available for kernel scheduling and ready to receive + interrupts from devices. Its cleared when a CPU is brought down using + ``__cpu_disable()``, before which all OS services including interrupts are + migrated to another target CPU. + +``cpu_present_mask`` + Bitmap of CPUs currently present in the system. Not all + of them may be online. When physical hotplug is processed by the relevant + subsystem (e.g ACPI) can change and new bit either be added or removed + from the map depending on the event is hot-add/hot-remove. There are currently + no locking rules as of now. Typical usage is to init topology during boot, + at which time hotplug is disabled. + +You really don't need to manipulate any of the system CPU maps. They should +be read-only for most use. When setting up per-cpu resources almost always use +``cpu_possible_mask`` or ``for_each_possible_cpu()`` to iterate. To macro +``for_each_cpu()`` can be used to iterate over a custom CPU mask. + +Never use anything other than ``cpumask_t`` to represent bitmap of CPUs. + + +Using CPU hotplug +================= +The kernel option *CONFIG_HOTPLUG_CPU* needs to be enabled. It is currently +available on multiple architectures including ARM, MIPS, PowerPC and X86. The +configuration is done via the sysfs interface: :: + + $ ls -lh /sys/devices/system/cpu + total 0 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu0 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu1 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu2 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu3 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu4 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu5 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu6 + drwxr-xr-x 9 root root 0 Dec 21 16:33 cpu7 + drwxr-xr-x 2 root root 0 Dec 21 16:33 hotplug + -r--r--r-- 1 root root 4.0K Dec 21 16:33 offline + -r--r--r-- 1 root root 4.0K Dec 21 16:33 online + -r--r--r-- 1 root root 4.0K Dec 21 16:33 possible + -r--r--r-- 1 root root 4.0K Dec 21 16:33 present + +The files *offline*, *online*, *possible*, *present* represent the CPU masks. +Each CPU folder contains an *online* file which controls the logical on (1) and +off (0) state. To logically shutdown CPU4: :: + + $ echo 0 > /sys/devices/system/cpu/cpu4/online + smpboot: CPU 4 is now offline + +Once the CPU is shutdown, it will be removed from */proc/interrupts*, +*/proc/cpuinfo* and should also not be shown visible by the *top* command. To +bring CPU4 back online: :: + + $ echo 1 > /sys/devices/system/cpu/cpu4/online + smpboot: Booting Node 0 Processor 4 APIC 0x1 + +The CPU is usable again. This should work on all CPUs. CPU0 is often special +and excluded from CPU hotplug. On X86 the kernel option +*CONFIG_BOOTPARAM_HOTPLUG_CPU0* has to be enabled in order to be able to +shutdown CPU0. Alternatively the kernel command option *cpu0_hotplug* can be +used. Some known dependencies of CPU0: + +* Resume from hibernate/suspend. Hibernate/suspend will fail if CPU0 is offline. +* PIC interrupts. CPU0 can't be removed if a PIC interrupt is detected. + +Please let Fenghua Yu know if you find any dependencies +on CPU0. + +The CPU hotplug coordination +============================ + +The offline case +---------------- +Once a CPU has been logically shutdown the teardown callbacks of registered +hotplug states will be invoked, starting with ``CPUHP_ONLINE`` and terminating +at state ``CPUHP_OFFLINE``. This includes: + +* If tasks are frozen due to a suspend operation then *cpuhp_tasks_frozen* + will be set to true. +* All processes are migrated away from this outgoing CPU to new CPUs. + The new CPU is chosen from each process' current cpuset, which may be + a subset of all online CPUs. +* All interrupts targeted to this CPU are migrated to a new CPU +* timers are also migrated to a new CPU +* Once all services are migrated, kernel calls an arch specific routine + ``__cpu_disable()`` to perform arch specific cleanup. + +Using the hotplug API +--------------------- +It is possible to receive notifications once a CPU is offline or onlined. This +might be important to certain drivers which need to perform some kind of setup +or clean up functions based on the number of available CPUs: :: + + #include + + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "X/Y:online", + Y_online, Y_prepare_down); + +*X* is the subsystem and *Y* the particular driver. The *Y_online* callback +will be invoked during registration on all online CPUs. If an error +occurs during the online callback the *Y_prepare_down* callback will be +invoked on all CPUs on which the online callback was previously invoked. +After registration completed, the *Y_online* callback will be invoked +once a CPU is brought online and *Y_prepare_down* will be invoked when a +CPU is shutdown. All resources which were previously allocated in +*Y_online* should be released in *Y_prepare_down*. +The return value *ret* is negative if an error occurred during the +registration process. Otherwise a positive value is returned which +contains the allocated hotplug for dynamically allocated states +(*CPUHP_AP_ONLINE_DYN*). It will return zero for predefined states. + +The callback can be remove by invoking ``cpuhp_remove_state()``. In case of a +dynamically allocated state (*CPUHP_AP_ONLINE_DYN*) use the returned state. +During the removal of a hotplug state the teardown callback will be invoked. + +Multiple instances +~~~~~~~~~~~~~~~~~~ +If a driver has multiple instances and each instance needs to perform the +callback independently then it is likely that a ''multi-state'' should be used. +First a multi-state state needs to be registered: :: + + ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "X/Y:online, + Y_online, Y_prepare_down); + Y_hp_online = ret; + +The ``cpuhp_setup_state_multi()`` behaves similar to ``cpuhp_setup_state()`` +except it prepares the callbacks for a multi state and does not invoke +the callbacks. This is a one time setup. +Once a new instance is allocated, you need to register this new instance: :: + + ret = cpuhp_state_add_instance(Y_hp_online, &d->node); + +This function will add this instance to your previously allocated +*Y_hp_online* state and invoke the previously registered callback +(*Y_online*) on all online CPUs. The *node* element is a ``struct +hlist_node`` member of your per-instance data structure. + +On removal of the instance: :: + cpuhp_state_remove_instance(Y_hp_online, &d->node) + +should be invoked which will invoke the teardown callback on all online +CPUs. + +Manual setup +~~~~~~~~~~~~ +Usually it is handy to invoke setup and teardown callbacks on registration or +removal of a state because usually the operation needs to performed once a CPU +goes online (offline) and during initial setup (shutdown) of the driver. However +each registration and removal function is also available with a ``_nocalls`` +suffix which does not invoke the provided callbacks if the invocation of the +callbacks is not desired. During the manual setup (or teardown) the functions +``get_online_cpus()`` and ``put_online_cpus()`` should be used to inhibit CPU +hotplug operations. + + +The ordering of the events +-------------------------- +The hotplug states are defined in ``include/linux/cpuhotplug.h``: + +* The states *CPUHP_OFFLINE* … *CPUHP_AP_OFFLINE* are invoked before the + CPU is up. +* The states *CPUHP_AP_OFFLINE* … *CPUHP_AP_ONLINE* are invoked + just the after the CPU has been brought up. The interrupts are off and + the scheduler is not yet active on this CPU. Starting with *CPUHP_AP_OFFLINE* + the callbacks are invoked on the target CPU. +* The states between *CPUHP_AP_ONLINE_DYN* and *CPUHP_AP_ONLINE_DYN_END* are + reserved for the dynamic allocation. +* The states are invoked in the reverse order on CPU shutdown starting with + *CPUHP_ONLINE* and stopping at *CPUHP_OFFLINE*. Here the callbacks are + invoked on the CPU that will be shutdown until *CPUHP_AP_OFFLINE*. + +A dynamically allocated state via *CPUHP_AP_ONLINE_DYN* is often enough. +However if an earlier invocation during the bring up or shutdown is required +then an explicit state should be acquired. An explicit state might also be +required if the hotplug event requires specific ordering in respect to +another hotplug event. + +Testing of hotplug states +========================= +One way to verify whether a custom state is working as expected or not is to +shutdown a CPU and then put it online again. It is also possible to put the CPU +to certain state (for instance *CPUHP_AP_ONLINE*) and then go back to +*CPUHP_ONLINE*. This would simulate an error one state after *CPUHP_AP_ONLINE* +which would lead to rollback to the online state. + +All registered states are enumerated in ``/sys/devices/system/cpu/hotplug/states``: :: + + $ tail /sys/devices/system/cpu/hotplug/states + 138: mm/vmscan:online + 139: mm/vmstat:online + 140: lib/percpu_cnt:online + 141: acpi/cpu-drv:online + 142: base/cacheinfo:online + 143: virtio/net:online + 144: x86/mce:online + 145: printk:online + 168: sched:active + 169: online + +To rollback CPU4 to ``lib/percpu_cnt:online`` and back online just issue: :: + + $ cat /sys/devices/system/cpu/cpu4/hotplug/state + 169 + $ echo 140 > /sys/devices/system/cpu/cpu4/hotplug/target + $ cat /sys/devices/system/cpu/cpu4/hotplug/state + 140 + +It is important to note that the teardown callbac of state 140 have been +invoked. And now get back online: :: + + $ echo 169 > /sys/devices/system/cpu/cpu4/hotplug/target + $ cat /sys/devices/system/cpu/cpu4/hotplug/state + 169 + +With trace events enabled, the individual steps are visible, too: :: + + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + bash-394 [001] 22.976: cpuhp_enter: cpu: 0004 target: 140 step: 169 (cpuhp_kick_ap_work) + cpuhp/4-31 [004] 22.977: cpuhp_enter: cpu: 0004 target: 140 step: 168 (sched_cpu_deactivate) + cpuhp/4-31 [004] 22.990: cpuhp_exit: cpu: 0004 state: 168 step: 168 ret: 0 + cpuhp/4-31 [004] 22.991: cpuhp_enter: cpu: 0004 target: 140 step: 144 (mce_cpu_pre_down) + cpuhp/4-31 [004] 22.992: cpuhp_exit: cpu: 0004 state: 144 step: 144 ret: 0 + cpuhp/4-31 [004] 22.993: cpuhp_multi_enter: cpu: 0004 target: 140 step: 143 (virtnet_cpu_down_prep) + cpuhp/4-31 [004] 22.994: cpuhp_exit: cpu: 0004 state: 143 step: 143 ret: 0 + cpuhp/4-31 [004] 22.995: cpuhp_enter: cpu: 0004 target: 140 step: 142 (cacheinfo_cpu_pre_down) + cpuhp/4-31 [004] 22.996: cpuhp_exit: cpu: 0004 state: 142 step: 142 ret: 0 + bash-394 [001] 22.997: cpuhp_exit: cpu: 0004 state: 140 step: 169 ret: 0 + bash-394 [005] 95.540: cpuhp_enter: cpu: 0004 target: 169 step: 140 (cpuhp_kick_ap_work) + cpuhp/4-31 [004] 95.541: cpuhp_enter: cpu: 0004 target: 169 step: 141 (acpi_soft_cpu_online) + cpuhp/4-31 [004] 95.542: cpuhp_exit: cpu: 0004 state: 141 step: 141 ret: 0 + cpuhp/4-31 [004] 95.543: cpuhp_enter: cpu: 0004 target: 169 step: 142 (cacheinfo_cpu_online) + cpuhp/4-31 [004] 95.544: cpuhp_exit: cpu: 0004 state: 142 step: 142 ret: 0 + cpuhp/4-31 [004] 95.545: cpuhp_multi_enter: cpu: 0004 target: 169 step: 143 (virtnet_cpu_online) + cpuhp/4-31 [004] 95.546: cpuhp_exit: cpu: 0004 state: 143 step: 143 ret: 0 + cpuhp/4-31 [004] 95.547: cpuhp_enter: cpu: 0004 target: 169 step: 144 (mce_cpu_online) + cpuhp/4-31 [004] 95.548: cpuhp_exit: cpu: 0004 state: 144 step: 144 ret: 0 + cpuhp/4-31 [004] 95.549: cpuhp_enter: cpu: 0004 target: 169 step: 145 (console_cpu_notify) + cpuhp/4-31 [004] 95.550: cpuhp_exit: cpu: 0004 state: 145 step: 145 ret: 0 + cpuhp/4-31 [004] 95.551: cpuhp_enter: cpu: 0004 target: 169 step: 168 (sched_cpu_activate) + cpuhp/4-31 [004] 95.552: cpuhp_exit: cpu: 0004 state: 168 step: 168 ret: 0 + bash-394 [005] 95.553: cpuhp_exit: cpu: 0004 state: 169 step: 140 ret: 0 + +As it an be seen, CPU4 went down until timestamp 22.996 and then back up until +95.552. All invoked callbacks including their return codes are visible in the +trace. + +Architecture's requirements +=========================== +The following functions and configurations are required: + +``CONFIG_HOTPLUG_CPU`` + This entry needs to be enabled in Kconfig + +``__cpu_up()`` + Arch interface to bring up a CPU + +``__cpu_disable()`` + Arch interface to shutdown a CPU, no more interrupts can be handled by the + kernel after the routine returns. This includes the shutdown of the timer. + +``__cpu_die()`` + This actually supposed to ensure death of the CPU. Actually look at some + example code in other arch that implement CPU hotplug. The processor is taken + down from the ``idle()`` loop for that specific architecture. ``__cpu_die()`` + typically waits for some per_cpu state to be set, to ensure the processor dead + routine is called to be sure positively. + +User Space Notification +======================= +After CPU successfully onlined or offline udev events are sent. A udev rule like: :: + + SUBSYSTEM=="cpu", DRIVERS=="processor", DEVPATH=="/devices/system/cpu/*", RUN+="the_hotplug_receiver.sh" + +will receive all events. A script like: :: + + #!/bin/sh + + if [ "${ACTION}" = "offline" ] + then + echo "CPU ${DEVPATH##*/} offline" + + elif [ "${ACTION}" = "online" ] + then + echo "CPU ${DEVPATH##*/} online" + + fi + +can process the event further. + +Kernel Inline Documentations Reference +====================================== + +.. kernel-doc:: include/linux/cpuhotplug.h diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst index 2872ca1a52f1..0d93d8089136 100644 --- a/Documentation/core-api/index.rst +++ b/Documentation/core-api/index.rst @@ -13,6 +13,7 @@ Core utilities assoc_array atomic_ops + cpu_hotplug local_ops workqueue diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt deleted file mode 100644 index d02e8a451872..000000000000 --- a/Documentation/cpu-hotplug.txt +++ /dev/null @@ -1,452 +0,0 @@ - CPU hotplug Support in Linux(tm) Kernel - - Maintainers: - CPU Hotplug Core: - Rusty Russell - Srivatsa Vaddagiri - i386: - Zwane Mwaikambo - ppc64: - Nathan Lynch - Joel Schopp - ia64/x86_64: - Ashok Raj - s390: - Heiko Carstens - -Authors: Ashok Raj -Lots of feedback: Nathan Lynch , - Joel Schopp - -Introduction - -Modern advances in system architectures have introduced advanced error -reporting and correction capabilities in processors. CPU architectures permit -partitioning support, where compute resources of a single CPU could be made -available to virtual machine environments. There are couple OEMS that -support NUMA hardware which are hot pluggable as well, where physical -node insertion and removal require support for CPU hotplug. - -Such advances require CPUs available to a kernel to be removed either for -provisioning reasons, or for RAS purposes to keep an offending CPU off -system execution path. Hence the need for CPU hotplug support in the -Linux kernel. - -A more novel use of CPU-hotplug support is its use today in suspend -resume support for SMP. Dual-core and HT support makes even -a laptop run SMP kernels which didn't support these methods. SMP support -for suspend/resume is a work in progress. - -General Stuff about CPU Hotplug --------------------------------- - -Command Line Switches ---------------------- -maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using - maxcpus=2 will only boot 2. You can choose to bring the - other cpus later online, read FAQ's for more info. - -additional_cpus=n (*) Use this to limit hotpluggable cpus. This option sets - cpu_possible_mask = cpu_present_mask + additional_cpus - -cede_offline={"off","on"} Use this option to disable/enable putting offlined - processors to an extended H_CEDE state on - supported pseries platforms. - If nothing is specified, - cede_offline is set to "on". - -(*) Option valid only for following architectures -- ia64 - -ia64 uses the number of disabled local apics in ACPI tables MADT to -determine the number of potentially hot-pluggable cpus. The implementation -should only rely on this to count the # of cpus, but *MUST* not rely -on the apicid values in those tables for disabled apics. In the event -BIOS doesn't mark such hot-pluggable cpus as disabled entries, one could -use this parameter "additional_cpus=x" to represent those cpus in the -cpu_possible_mask. - -possible_cpus=n [s390,x86_64] use this to set hotpluggable cpus. - This option sets possible_cpus bits in - cpu_possible_mask. Thus keeping the numbers of bits set - constant even if the machine gets rebooted. - -CPU maps and such ------------------ -[More on cpumaps and primitive to manipulate, please check -include/linux/cpumask.h that has more descriptive text.] - -cpu_possible_mask: Bitmap of possible CPUs that can ever be available in the -system. This is used to allocate some boot time memory for per_cpu variables -that aren't designed to grow/shrink as CPUs are made available or removed. -Once set during boot time discovery phase, the map is static, i.e no bits -are added or removed anytime. Trimming it accurately for your system needs -upfront can save some boot time memory. See below for how we use heuristics -in x86_64 case to keep this under check. - -cpu_online_mask: Bitmap of all CPUs currently online. It's set in __cpu_up() -after a CPU is available for kernel scheduling and ready to receive -interrupts from devices. It's cleared when a CPU is brought down using -__cpu_disable(), before which all OS services including interrupts are -migrated to another target CPU. - -cpu_present_mask: Bitmap of CPUs currently present in the system. Not all -of them may be online. When physical hotplug is processed by the relevant -subsystem (e.g ACPI) can change and new bit either be added or removed -from the map depending on the event is hot-add/hot-remove. There are currently -no locking rules as of now. Typical usage is to init topology during boot, -at which time hotplug is disabled. - -You really dont need to manipulate any of the system cpu maps. They should -be read-only for most use. When setting up per-cpu resources almost always use -cpu_possible_mask/for_each_possible_cpu() to iterate. - -Never use anything other than cpumask_t to represent bitmap of CPUs. - - #include - - for_each_possible_cpu - Iterate over cpu_possible_mask - for_each_online_cpu - Iterate over cpu_online_mask - for_each_present_cpu - Iterate over cpu_present_mask - for_each_cpu(x,mask) - Iterate over some random collection of cpu mask. - - #include - get_online_cpus() and put_online_cpus(): - -The above calls are used to inhibit cpu hotplug operations. While the -cpu_hotplug.refcount is non zero, the cpu_online_mask will not change. -If you merely need to avoid cpus going away, you could also use -preempt_disable() and preempt_enable() for those sections. -Just remember the critical section cannot call any -function that can sleep or schedule this process away. The preempt_disable() -will work as long as stop_machine_run() is used to take a cpu down. - -CPU Hotplug - Frequently Asked Questions. - -Q: How to enable my kernel to support CPU hotplug? -A: When doing make defconfig, Enable CPU hotplug support - - "Processor type and Features" -> Support for Hotpluggable CPUs - -Make sure that you have CONFIG_SMP turned on as well. - -You would need to enable CONFIG_HOTPLUG_CPU for SMP suspend/resume support -as well. - -Q: What architectures support CPU hotplug? -A: As of 2.6.14, the following architectures support CPU hotplug. - -i386 (Intel), ppc, ppc64, parisc, s390, ia64 and x86_64 - -Q: How to test if hotplug is supported on the newly built kernel? -A: You should now notice an entry in sysfs. - -Check if sysfs is mounted, using the "mount" command. You should notice -an entry as shown below in the output. - - .... - none on /sys type sysfs (rw) - .... - -If this is not mounted, do the following. - - #mkdir /sys - #mount -t sysfs sys /sys - -Now you should see entries for all present cpu, the following is an example -in a 8-way system. - - #pwd - #/sys/devices/system/cpu - #ls -l - total 0 - drwxr-xr-x 10 root root 0 Sep 19 07:44 . - drwxr-xr-x 13 root root 0 Sep 19 07:45 .. - drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu0 - drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu1 - drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu2 - drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu3 - drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu4 - drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu5 - drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu6 - drwxr-xr-x 3 root root 0 Sep 19 07:48 cpu7 - -Under each directory you would find an "online" file which is the control -file to logically online/offline a processor. - -Q: Does hot-add/hot-remove refer to physical add/remove of cpus? -A: The usage of hot-add/remove may not be very consistently used in the code. -CONFIG_HOTPLUG_CPU enables logical online/offline capability in the kernel. -To support physical addition/removal, one would need some BIOS hooks and -the platform should have something like an attention button in PCI hotplug. -CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of CPUs. - -Q: How do I logically offline a CPU? -A: Do the following. - - #echo 0 > /sys/devices/system/cpu/cpuX/online - -Once the logical offline is successful, check - - #cat /proc/interrupts - -You should now not see the CPU that you removed. Also online file will report -the state as 0 when a CPU is offline and 1 when it's online. - - #To display the current cpu state. - #cat /sys/devices/system/cpu/cpuX/online - -Q: Why can't I remove CPU0 on some systems? -A: Some architectures may have some special dependency on a certain CPU. - -For e.g in IA64 platforms we have ability to send platform interrupts to the -OS. a.k.a Corrected Platform Error Interrupts (CPEI). In current ACPI -specifications, we didn't have a way to change the target CPU. Hence if the -current ACPI version doesn't support such re-direction, we disable that CPU -by making it not-removable. - -In such cases you will also notice that the online file is missing under cpu0. - -Q: Is CPU0 removable on X86? -A: Yes. If kernel is compiled with CONFIG_BOOTPARAM_HOTPLUG_CPU0=y, CPU0 is -removable by default. Otherwise, CPU0 is also removable by kernel option -cpu0_hotplug. - -But some features depend on CPU0. Two known dependencies are: - -1. Resume from hibernate/suspend depends on CPU0. Hibernate/suspend will fail if -CPU0 is offline and you need to online CPU0 before hibernate/suspend can -continue. -2. PIC interrupts also depend on CPU0. CPU0 can't be removed if a PIC interrupt -is detected. - -It's said poweroff/reboot may depend on CPU0 on some machines although I haven't -seen any poweroff/reboot failure so far after CPU0 is offline on a few tested -machines. - -Please let me know if you know or see any other dependencies of CPU0. - -If the dependencies are under your control, you can turn on CPU0 hotplug feature -either by CONFIG_BOOTPARAM_HOTPLUG_CPU0 or by kernel parameter cpu0_hotplug. - ---Fenghua Yu - -Q: How do I find out if a particular CPU is not removable? -A: Depending on the implementation, some architectures may show this by the -absence of the "online" file. This is done if it can be determined ahead of -time that this CPU cannot be removed. - -In some situations, this can be a run time check, i.e if you try to remove the -last CPU, this will not be permitted. You can find such failures by -investigating the return value of the "echo" command. - -Q: What happens when a CPU is being logically offlined? -A: The following happen, listed in no particular order :-) - -- A notification is sent to in-kernel registered modules by sending an event - CPU_DOWN_PREPARE or CPU_DOWN_PREPARE_FROZEN, depending on whether or not the - CPU is being offlined while tasks are frozen due to a suspend operation in - progress -- All processes are migrated away from this outgoing CPU to new CPUs. - The new CPU is chosen from each process' current cpuset, which may be - a subset of all online CPUs. -- All interrupts targeted to this CPU are migrated to a new CPU -- timers/bottom half/task lets are also migrated to a new CPU -- Once all services are migrated, kernel calls an arch specific routine - __cpu_disable() to perform arch specific cleanup. -- Once this is successful, an event for successful cleanup is sent by an event - CPU_DEAD (or CPU_DEAD_FROZEN if tasks are frozen due to a suspend while the - CPU is being offlined). - - "It is expected that each service cleans up when the CPU_DOWN_PREPARE - notifier is called, when CPU_DEAD is called it's expected there is nothing - running on behalf of this CPU that was offlined" - -Q: If I have some kernel code that needs to be aware of CPU arrival and - departure, how to i arrange for proper notification? -A: This is what you would need in your kernel code to receive notifications. - - #include - static int foobar_cpu_callback(struct notifier_block *nfb, - unsigned long action, void *hcpu) - { - unsigned int cpu = (unsigned long)hcpu; - - switch (action) { - case CPU_ONLINE: - case CPU_ONLINE_FROZEN: - foobar_online_action(cpu); - break; - case CPU_DEAD: - case CPU_DEAD_FROZEN: - foobar_dead_action(cpu); - break; - } - return NOTIFY_OK; - } - - static struct notifier_block foobar_cpu_notifier = - { - .notifier_call = foobar_cpu_callback, - }; - -You need to call register_cpu_notifier() from your init function. -Init functions could be of two types: -1. early init (init function called when only the boot processor is online). -2. late init (init function called _after_ all the CPUs are online). - -For the first case, you should add the following to your init function - - register_cpu_notifier(&foobar_cpu_notifier); - -For the second case, you should add the following to your init function - - register_hotcpu_notifier(&foobar_cpu_notifier); - -You can fail PREPARE notifiers if something doesn't work to prepare resources. -This will stop the activity and send a following CANCELED event back. - -CPU_DEAD should not be failed, its just a goodness indication, but bad -things will happen if a notifier in path sent a BAD notify code. - -Q: I don't see my action being called for all CPUs already up and running? -A: Yes, CPU notifiers are called only when new CPUs are on-lined or offlined. - If you need to perform some action for each CPU already in the system, then - do this: - - for_each_online_cpu(i) { - foobar_cpu_callback(&foobar_cpu_notifier, CPU_UP_PREPARE, i); - foobar_cpu_callback(&foobar_cpu_notifier, CPU_ONLINE, i); - } - - However, if you want to register a hotplug callback, as well as perform - some initialization for CPUs that are already online, then do this: - - Version 1: (Correct) - --------- - - cpu_notifier_register_begin(); - - for_each_online_cpu(i) { - foobar_cpu_callback(&foobar_cpu_notifier, - CPU_UP_PREPARE, i); - foobar_cpu_callback(&foobar_cpu_notifier, - CPU_ONLINE, i); - } - - /* Note the use of the double underscored version of the API */ - __register_cpu_notifier(&foobar_cpu_notifier); - - cpu_notifier_register_done(); - - Note that the following code is *NOT* the right way to achieve this, - because it is prone to an ABBA deadlock between the cpu_add_remove_lock - and the cpu_hotplug.lock. - - Version 2: (Wrong!) - --------- - - get_online_cpus(); - - for_each_online_cpu(i) { - foobar_cpu_callback(&foobar_cpu_notifier, - CPU_UP_PREPARE, i); - foobar_cpu_callback(&foobar_cpu_notifier, - CPU_ONLINE, i); - } - - register_cpu_notifier(&foobar_cpu_notifier); - - put_online_cpus(); - - So always use the first version shown above when you want to register - callbacks as well as initialize the already online CPUs. - - -Q: If I would like to develop CPU hotplug support for a new architecture, - what do I need at a minimum? -A: The following are what is required for CPU hotplug infrastructure to work - correctly. - - - Make sure you have an entry in Kconfig to enable CONFIG_HOTPLUG_CPU - - __cpu_up() - Arch interface to bring up a CPU - - __cpu_disable() - Arch interface to shutdown a CPU, no more interrupts - can be handled by the kernel after the routine - returns. Including local APIC timers etc are - shutdown. - - __cpu_die() - This actually supposed to ensure death of the CPU. - Actually look at some example code in other arch - that implement CPU hotplug. The processor is taken - down from the idle() loop for that specific - architecture. __cpu_die() typically waits for some - per_cpu state to be set, to ensure the processor - dead routine is called to be sure positively. - -Q: I need to ensure that a particular CPU is not removed when there is some - work specific to this CPU in progress. -A: There are two ways. If your code can be run in interrupt context, use - smp_call_function_single(), otherwise use work_on_cpu(). Note that - work_on_cpu() is slow, and can fail due to out of memory: - - int my_func_on_cpu(int cpu) - { - int err; - get_online_cpus(); - if (!cpu_online(cpu)) - err = -EINVAL; - else -#if NEEDS_BLOCKING - err = work_on_cpu(cpu, __my_func_on_cpu, NULL); -#else - smp_call_function_single(cpu, __my_func_on_cpu, &err, - true); -#endif - put_online_cpus(); - return err; - } - -Q: How do we determine how many CPUs are available for hotplug. -A: There is no clear spec defined way from ACPI that can give us that - information today. Based on some input from Natalie of Unisys, - that the ACPI MADT (Multiple APIC Description Tables) marks those possible - CPUs in a system with disabled status. - - Andi implemented some simple heuristics that count the number of disabled - CPUs in MADT as hotpluggable CPUS. In the case there are no disabled CPUS - we assume 1/2 the number of CPUs currently present can be hotplugged. - - Caveat: ACPI MADT can only provide 256 entries in systems with only ACPI 2.0c - or earlier ACPI version supported, because the apicid field in MADT is only - 8 bits. From ACPI 3.0, this limitation was removed since the apicid field - was extended to 32 bits with x2APIC introduced. - -User Space Notification - -Hotplug support for devices is common in Linux today. Its being used today to -support automatic configuration of network, usb and pci devices. A hotplug -event can be used to invoke an agent script to perform the configuration task. - -You can add /etc/hotplug/cpu.agent to handle hotplug notification user space -scripts. - - #!/bin/bash - # $Id: cpu.agent - # Kernel hotplug params include: - #ACTION=%s [online or offline] - #DEVPATH=%s - # - cd /etc/hotplug - . ./hotplug.functions - - case $ACTION in - online) - echo `date` ":cpu.agent" add cpu >> /tmp/hotplug.txt - ;; - offline) - echo `date` ":cpu.agent" remove cpu >>/tmp/hotplug.txt - ;; - *) - debug_mesg CPU $ACTION event not supported - exit 1 - ;; - esac -- cgit v1.2.3 From e57ae44a584f6d574b45d40a036b8c7ddd5d0feb Mon Sep 17 00:00:00 2001 From: Sanjeev Date: Wed, 11 Jan 2017 02:28:40 +0800 Subject: Doc: clarify that GPL is GPL v2, not v2+ ... and a minor missing period at EOL Signed-off-by: Sanjeev Gupta Signed-off-by: Jonathan Corbet --- Documentation/admin-guide/README.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/admin-guide/README.rst b/Documentation/admin-guide/README.rst index 1b6dfb2b3adb..697a00ccec25 100644 --- a/Documentation/admin-guide/README.rst +++ b/Documentation/admin-guide/README.rst @@ -17,7 +17,7 @@ What is Linux? loading, shared copy-on-write executables, proper memory management, and multistack networking including IPv4 and IPv6. - It is distributed under the GNU General Public License - see the + It is distributed under the GNU General Public License v2 - see the accompanying COPYING file for more details. On what hardware does it run? @@ -236,7 +236,7 @@ Configuring the kernel - Having unnecessary drivers will make the kernel bigger, and can under some circumstances lead to problems: probing for a - nonexistent controller card may confuse your other controllers + nonexistent controller card may confuse your other controllers. - A kernel with math-emulation compiled in will still use the coprocessor if one is present: the math emulation will just -- cgit v1.2.3 From 43d8808b0820df056e7cfc7cc374d5a20fd37546 Mon Sep 17 00:00:00 2001 From: "W. Trevor King" Date: Thu, 12 Jan 2017 14:24:27 -0800 Subject: Documentation: cpuset: Fix 'cpuset.tasks' -> 'tasks' This looks like it was accidentally caught up in e21a05cb (doc: cpuset: Update the cpuset flag file, 2010-02-24). While I'm touching the line, also fix the posessive "cpusets" -> "cpuset's". Signed-off-by: W. Trevor King Signed-off-by: Jonathan Corbet --- Documentation/cgroup-v1/cpusets.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/cgroup-v1/cpusets.txt b/Documentation/cgroup-v1/cpusets.txt index e5ac5da86682..8402dd6de8df 100644 --- a/Documentation/cgroup-v1/cpusets.txt +++ b/Documentation/cgroup-v1/cpusets.txt @@ -615,7 +615,7 @@ to allocate a page of memory for that task. If a cpuset has its 'cpuset.cpus' modified, then each task in that cpuset will have its allowed CPU placement changed immediately. Similarly, -if a task's pid is written to another cpusets 'cpuset.tasks' file, then its +if a task's pid is written to another cpuset's 'tasks' file, then its allowed CPU placement is changed immediately. If such a task had been bound to some subset of its cpuset using the sched_setaffinity() call, the task will be allowed to run on any CPU allowed in its new cpuset, -- cgit v1.2.3 From c80c45019957dcb226f549ebfbeaa9ef7b4eb8c5 Mon Sep 17 00:00:00 2001 From: Florian Fainelli Date: Mon, 16 Jan 2017 14:31:15 -0800 Subject: Documentation: dontdiff: Update with additional entries Add a bunch of entries reflective of programs that the kernel build: sortextable, dtc. And while at it, expand the lex*.c entries to cover e.g: dtc-lexer.c. Finally, exclude devicetable-offsets.h Signed-off-by: Florian Fainelli Signed-off-by: Jonathan Corbet --- Documentation/dontdiff | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/dontdiff b/Documentation/dontdiff index a23edccd2059..77b92221f951 100644 --- a/Documentation/dontdiff +++ b/Documentation/dontdiff @@ -116,9 +116,11 @@ crc32table.h* cscope.* defkeymap.c devlist.h* +devicetable-offsets.h dnotify_test docproc dslm +dtc elf2ecoff elfconfig.h* evergreen_reg_safe.h @@ -153,8 +155,8 @@ keywords.c ksym.c* ksym.h* kxgettext -lex.c -lex.*.c +*lex.c +*lex.*.c linux logo_*.c logo_*_clut224.c @@ -215,6 +217,7 @@ series setup setup.bin setup.elf +sortextable sImage sm_tbl* split-include -- cgit v1.2.3 From 31fc93d5f29b300307cda5aef95d890954337e01 Mon Sep 17 00:00:00 2001 From: Steven Price Date: Tue, 17 Jan 2017 13:38:49 +0000 Subject: dynamic-debug-howto: Correct echo -c to -n Two of the example command lines use an argument to echo of "-c" which isn't valid in (most versions of) echo causing these examples to fail. Correct the argument to "-n" which works correctly. Signed-off-by: Steven Price Signed-off-by: Jonathan Corbet --- Documentation/admin-guide/dynamic-debug-howto.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst index 88adcfdf5b2b..12278a926370 100644 --- a/Documentation/admin-guide/dynamic-debug-howto.rst +++ b/Documentation/admin-guide/dynamic-debug-howto.rst @@ -93,9 +93,9 @@ Command Language Reference At the lexical level, a command comprises a sequence of words separated by spaces or tabs. So these are all equivalent:: - nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' > + nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > /dynamic_debug/control - nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' > + nullarbor:~ # echo -n ' file svcsock.c line 1603 +p ' > /dynamic_debug/control nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > /dynamic_debug/control -- cgit v1.2.3 From 8da9704c8bb7d4b0a2b051a5a7eda9b049f5f766 Mon Sep 17 00:00:00 2001 From: Masanari Iida Date: Tue, 24 Jan 2017 21:45:15 +0900 Subject: Doc: Fix double words in Documentation This patch fix some double words found in Documentation. Signed-off-by: Masanari Iida Signed-off-by: Jonathan Corbet --- Documentation/block/pr.txt | 2 +- Documentation/ioctl/botching-up-ioctls.txt | 2 +- Documentation/livepatch/livepatch.txt | 2 +- Documentation/networking/kcm.txt | 2 +- Documentation/usb/power-management.txt | 2 +- Documentation/vm/transhuge.txt | 2 +- 6 files changed, 6 insertions(+), 6 deletions(-) (limited to 'Documentation') diff --git a/Documentation/block/pr.txt b/Documentation/block/pr.txt index d3eb1ca65051..ac9b8e70e64b 100644 --- a/Documentation/block/pr.txt +++ b/Documentation/block/pr.txt @@ -90,7 +90,7 @@ and thus removes any access restriction implied by it. 4. IOC_PR_PREEMPT This ioctl command releases the existing reservation referred to by -old_key and replaces it with a a new reservation of type for the +old_key and replaces it with a new reservation of type for the reservation key new_key. diff --git a/Documentation/ioctl/botching-up-ioctls.txt b/Documentation/ioctl/botching-up-ioctls.txt index 36138c632f7a..d02cfb48901c 100644 --- a/Documentation/ioctl/botching-up-ioctls.txt +++ b/Documentation/ioctl/botching-up-ioctls.txt @@ -24,7 +24,7 @@ Prerequisites ------------- First the prerequisites. Without these you have already failed, because you -will need to add a a 32-bit compat layer: +will need to add a 32-bit compat layer: * Only use fixed sized integers. To avoid conflicts with typedefs in userspace the kernel has special types like __u32, __s64. Use them. diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt index f5967316deb9..cbfabd188779 100644 --- a/Documentation/livepatch/livepatch.txt +++ b/Documentation/livepatch/livepatch.txt @@ -377,7 +377,7 @@ The current Livepatch implementation has several limitations: Each function has to handle TOC and save LR before it could call the ftrace handler. This operation has to be reverted on return. Fortunately, the generic ftrace code has the same problem and all - this is is handled on the ftrace level. + this is handled on the ftrace level. + Kretprobes using the ftrace framework conflict with the patched diff --git a/Documentation/networking/kcm.txt b/Documentation/networking/kcm.txt index 3476ede5bc2c..9a513295b07c 100644 --- a/Documentation/networking/kcm.txt +++ b/Documentation/networking/kcm.txt @@ -272,7 +272,7 @@ on the socket thus waking up the application thread. When the application sees the error (which may just be a disconnect) it should unattach the socket from KCM and then close it. It is assumed that once an error is posted on the TCP socket the data stream is unrecoverable (i.e. an error -may have occurred in in the middle of receiving a messssge). +may have occurred in the middle of receiving a messssge). TCP connection monitoring ------------------------- diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt index 0a94ffe17ab6..00e706997130 100644 --- a/Documentation/usb/power-management.txt +++ b/Documentation/usb/power-management.txt @@ -543,7 +543,7 @@ relevant attribute files are usb2_hardware_lpm and usb3_hardware_lpm. When a USB 3.0 lpm-capable device is plugged in to a xHCI host which supports link PM, it will check if U1 and U2 exit latencies have been set in the BOS - descriptor; if the check is is passed and the host + descriptor; if the check is passed and the host supports USB3 hardware LPM, USB3 hardware LPM will be enabled for the device and these files will be created. The files hold a string value (enable or disable) diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt index c4171e4519c2..f2e739545e74 100644 --- a/Documentation/vm/transhuge.txt +++ b/Documentation/vm/transhuge.txt @@ -296,7 +296,7 @@ thp_split_page is incremented every time a huge page is split into base reason is that a huge page is old and is being reclaimed. This action implies splitting all PMD the page mapped with. -thp_split_page_failed is is incremented if kernel fails to split huge +thp_split_page_failed is incremented if kernel fails to split huge page. This can happen if the page was pinned by somebody. thp_deferred_split_page is incremented when a huge page is put onto split -- cgit v1.2.3 From 9e5e74e61ce8615d4105b2651f6b7d46434014f2 Mon Sep 17 00:00:00 2001 From: Andy Deng Date: Wed, 25 Jan 2017 12:14:31 +0800 Subject: zh_CN/CodingStyle: improve translation Some of the sentences in Chapters 19 and 20 are re-translated: - Fixed translation errors in Section 2 of Chapter 19 to prevent misleading readers; - Retranslate some sentences to make the translation more clear and accurate. Signed-off-by: Andy Deng Signed-off-by: Jonathan Corbet --- Documentation/translations/zh_CN/CodingStyle | 61 ++++++++++++++-------------- 1 file changed, 31 insertions(+), 30 deletions(-) (limited to 'Documentation') diff --git a/Documentation/translations/zh_CN/CodingStyle b/Documentation/translations/zh_CN/CodingStyle index dc101f48e713..45b8fc9ef8ea 100644 --- a/Documentation/translations/zh_CN/CodingStyle +++ b/Documentation/translations/zh_CN/CodingStyle @@ -735,22 +735,22 @@ Vim 能够解释这样的标记： 第十九章：内联汇编 -在特定架构的代码中，你也许需要内联汇编来使用 CPU 接口和平台相关功能。在需要 -这么做时，不要犹豫。然而，当 C 可以完成工作时，不要无端地使用内联汇编。如果 -可能，你可以并且应该用 C 和硬件交互。 +在特定架构的代码中，你可能需要内联汇编与 CPU 和平台相关功能连接。需要这么做时 +就不要犹豫。然而，当 C 可以完成工作时，不要平白无故地使用内联汇编。在可能的情 +况下，你可以并且应该用 C 和硬件沟通。 -考虑去写通用一点的内联汇编作为简明的辅助函数，而不是重复写下它们的细节。记住 -内联汇编可以使用 C 参数。 +请考虑去写捆绑通用位元 (wrap common bits) 的内联汇编的简单辅助函数，别去重复 +地写下只有细微差异内联汇编。记住内联汇编可以使用 C 参数。 -大而特殊的汇编函数应该放在 .S 文件中，对应 C 的原型定义在 C 头文件中。汇编 -函数的 C 原型应该使用 “asmlinkage”。 +大型，有一定复杂度的汇编函数应该放在 .S 文件内，用相应的 C 原型定义在 C 头文 +件中。汇编函数的 C 原型应该使用 “asmlinkage”。 -你可能需要将你的汇编语句标记为 volatile，来阻止 GCC 在没发现任何副作用后就 -移除了它。你不必总是这样做，虽然，这样可以限制不必要的优化。 +你可能需要把汇编语句标记为 volatile，用来阻止 GCC 在没发现任何副作用后就把它 +移除了。你不必总是这样做，尽管，这不必要的举动会限制优化。 -在写一个包含多条指令的单个内联汇编语句时，把每条指令用引号字符串分离，并写在 -单独一行，在每个字符串结尾，除了 \n\t 结尾之外，在汇编输出中适当地缩进下 -一条指令： +在写一个包含多条指令的单个内联汇编语句时，把每条指令用引号分割而且各占一行， +除了最后一条指令外，在每个指令结尾加上 \n\t，让汇编输出时可以正确地缩进下一条 +指令： asm ("magic %reg1, #42\n\t" "more_magic %reg2, %reg3" @@ -759,33 +759,34 @@ Vim 能够解释这样的标记： 第二十章：条件编译 -只要可能，就不要在 .c 文件里面使用预处理条件；这样做让代码更难阅读并且逻辑难以 -跟踪。替代方案是，在头文件定义函数在这些 .c 文件中使用这类的条件表达式，提供空 -操作的桩版本（译注：桩程序，是指用来替换一部分功能的程序段）在 #else 情况下， -再从 .c 文件中无条件地调用这些函数。编译器会避免生成任何桩调用的代码，产生一致 -的结果，但逻辑将更加清晰。 +只要可能，就不要在 .c 文件里面使用预处理条件 (#if, #ifdef)；这样做让代码更难 +阅读并且更难去跟踪逻辑。替代方案是，在头文件中用预处理条件提供给那些 .c 文件 +使用，再给 #else 提供一个空桩 (no-op stub) 版本，然后在 .c 文件内无条件地调用 +那些 (定义在头文件内的) 函数。这样做，编译器会避免为桩函数 (stub) 的调用生成 +任何代码，产生的结果是相同的，但逻辑将更加清晰。 -宁可编译整个函数，而不是部分函数或部分表达式。而不是在一个表达式添加 ifdef， -解析部分或全部表达式到一个单独的辅助函数，并应用条件到该函数内。 +最好倾向于编译整个函数，而不是函数的一部分或表达式的一部分。与其放一个 ifdef +在表达式内，不如分解出部分或全部表达式，放进一个单独的辅助函数，并应用预处理 +条件到这个辅助函数内。 -如果你有一个在特定配置中可能是未使用的函数或变量，编译器将警告它定义了但未使用， -标记这个定义为 __maybe_unused 而不是将它包含在一个预处理条件中。（然而，如果 -一个函数或变量总是未使用的，就直接删除它。） +如果你有一个在特定配置中，可能变成未使用的函数或变量，编译器会警告它定义了但 +未使用，把它标记为 __maybe_unused 而不是将它包含在一个预处理条件中。(然而，如 +果一个函数或变量总是未使用，就直接删除它。) -在代码中，可能的情况下，使用 IS_ENABLED 宏来转化某个 Kconfig 标记为 C 的布尔 -表达式，并在正常的 C 条件中使用它： +在代码中，尽可能地使用 IS_ENABLED 宏来转化某个 Kconfig 标记为 C 的布尔 +表达式，并在一般的 C 条件中使用它： if (IS_ENABLED(CONFIG_SOMETHING)) { ... } -编译器会无条件地做常数合并，就像使用 #ifdef 那样，包含或排除代码块，所以这不会 -带来任何运行时开销。然而，这种方法依旧允许 C 编译器查看块内的代码，并检查它的正确 -性（语法，类型，符号引用，等等）。因此，如果条件不满足，代码块内的引用符号将不存在， -你必须继续使用 #ifdef。 +编译器会做常量折叠，然后就像使用 #ifdef 那样去包含或排除代码块，所以这不会带 +来任何运行时开销。然而，这种方法依旧允许 C 编译器查看块内的代码，并检查它的正 +确性 (语法，类型，符号引用，等等)。因此，如果条件不满足，代码块内的引用符号就 +不存在时，你还是必须去用 #ifdef。 -在任何有意义的 #if 或 #ifdef 块的末尾（超过几行），在 #endif 同一行的后面写下 -注释，指出该条件表达式被使用。例如： +在任何有意义的 #if 或 #ifdef 块的末尾 (超过几行的)，在 #endif 同一行的后面写 +下注解，注释这个条件表达式。例如： #ifdef CONFIG_SOMETHING ... -- cgit v1.2.3 From 0dacbc9df5c9fc6037060fbb12c1d7da80f5b580 Mon Sep 17 00:00:00 2001 From: Andy Deng Date: Wed, 25 Jan 2017 12:14:32 +0800 Subject: zh_CN/CodingStyle: Convert to ReST markup This commit applies all changes from the English version, and should be able to work with the documentation build system. Signed-off-by: Andy Deng Signed-off-by: Jonathan Corbet --- Documentation/translations/zh_CN/CodingStyle | 788 ++++++++++++++++----------- 1 file changed, 462 insertions(+), 326 deletions(-) (limited to 'Documentation') diff --git a/Documentation/translations/zh_CN/CodingStyle b/Documentation/translations/zh_CN/CodingStyle index 45b8fc9ef8ea..1466aa64b8b4 100644 --- a/Documentation/translations/zh_CN/CodingStyle +++ b/Documentation/translations/zh_CN/CodingStyle @@ -6,51 +6,61 @@ Chinese maintainer for help. Contact the Chinese maintainer, if this translation is outdated or there is problem with translation. Chinese maintainer: Zhang Le + --------------------------------------------------------------------- -Documentation/process/coding-style.rst的中文翻译 - -如果想评论或更新本文的内容，请直接发信到LKML。如果你使用英文交流有困难的话，也可 -以向中文版维护者求助。如果本翻译更新不及时或者翻译存在问题，请联系中文版维护者。 - -中文版维护者： 张乐 Zhang Le -中文版翻译者： 张乐 Zhang Le -中文版校译者： 王聪 Wang Cong - wheelz - 管旭东 Xudong Guan - Li Zefan - Wang Chen + +Documentation/process/coding-style.rst 的中文翻译 + +如果想评论或更新本文的内容，请直接发信到LKML。如果你使用英文交流有困难的话， +也可以向中文版维护者求助。如果本翻译更新不及时或者翻译存在问题，请联系中文版 +维护者:: + + 中文版维护者： 张乐 Zhang Le + 中文版翻译者： 张乐 Zhang Le + 中文版校译者： 王聪 Wang Cong + wheelz + 管旭东 Xudong Guan + Li Zefan + Wang Chen + 以下为正文 + --------------------------------------------------------------------- - Linux内核代码风格 +Linux 内核代码风格 +========================= -这是一个简短的文档，描述了 linux 内核的首选代码风格。代码风格是因人而异的，而且我 -不愿意把自己的观点强加给任何人，但这就像我去做任何事情都必须遵循的原则那样，我也 -希望在绝大多数事上保持这种的态度。请（在写代码时）至少考虑一下这里的代码风格。 +这是一个简短的文档，描述了 linux 内核的首选代码风格。代码风格是因人而异的， +而且我不愿意把自己的观点强加给任何人，但这就像我去做任何事情都必须遵循的原则 +那样，我也希望在绝大多数事上保持这种的态度。请 (在写代码时) 至少考虑一下这里 +的代码风格。 -首先，我建议你打印一份 GNU 代码规范，然后不要读。烧了它，这是一个具有重大象征性意义 -的动作。 +首先，我建议你打印一份 GNU 代码规范，然后不要读。烧了它，这是一个具有重大象征 +性意义的动作。 不管怎样，现在我们开始： - 第一章：缩进 +1) 缩进 +-------------- + +制表符是 8 个字符，所以缩进也是 8 个字符。有些异端运动试图将缩进变为 4 (甚至 +2！) 字符深，这几乎相当于尝试将圆周率的值定义为 3。 -制表符是 8 个字符，所以缩进也是 8 个字符。有些异端运动试图将缩进变为 4（甚至 2！） -个字符深，这几乎相当于尝试将圆周率的值定义为 3。 +理由：缩进的全部意义就在于清楚的定义一个控制块起止于何处。尤其是当你盯着你的 +屏幕连续看了 20 小时之后，你将会发现大一点的缩进会使你更容易分辨缩进。 -理由：缩进的全部意义就在于清楚的定义一个控制块起止于何处。尤其是当你盯着你的屏幕 -连续看了 20 小时之后，你将会发现大一点的缩进会使你更容易分辨缩进。 +现在，有些人会抱怨 8 个字符的缩进会使代码向右边移动的太远，在 80 个字符的终端 +屏幕上就很难读这样的代码。这个问题的答案是，如果你需要 3 级以上的缩进，不管用 +何种方式你的代码已经有问题了，应该修正你的程序。 -现在，有些人会抱怨 8 个字符的缩进会使代码向右边移动的太远，在 80 个字符的终端屏幕上 -就很难读这样的代码。这个问题的答案是，如果你需要 3 级以上的缩进，不管用何种方式你 -的代码已经有问题了，应该修正你的程序。 +简而言之，8 个字符的缩进可以让代码更容易阅读，还有一个好处是当你的函数嵌套太 +深的时候可以给你警告。留心这个警告。 -简而言之，8 个字符的缩进可以让代码更容易阅读，还有一个好处是当你的函数嵌套太深的 -时候可以给你警告。留心这个警告。 +在 switch 语句中消除多级缩进的首选的方式是让 ``switch`` 和从属于它的 ``case`` +标签对齐于同一列，而不要 ``两次缩进`` ``case`` 标签。比如： -在 switch 语句中消除多级缩进的首选的方式是让 “switch” 和从属于它的 “case” 标签 -对齐于同一列，而不要 “两次缩进” “case” 标签。比如： +.. code-block:: c switch (suffix) { case 'G': @@ -71,39 +81,49 @@ Documentation/process/coding-style.rst的中文翻译 不要把多个语句放在一行里，除非你有什么东西要隐藏： +.. code-block:: c + if (condition) do_this; do_something_everytime; -也不要在一行里放多个赋值语句。内核代码风格超级简单。就是避免可能导致别人误读的表 -达式。 +也不要在一行里放多个赋值语句。内核代码风格超级简单。就是避免可能导致别人误读 +的表达式。 -除了注释、文档和 Kconfig 之外，不要使用空格来缩进，前面的例子是例外，是有意为之。 +除了注释、文档和 Kconfig 之外，不要使用空格来缩进，前面的例子是例外，是有意为 +之。 选用一个好的编辑器，不要在行尾留空格。 - 第二章：把长的行和字符串打散 +2) 把长的行和字符串打散 +------------------------------ 代码风格的意义就在于使用平常使用的工具来维持代码的可读性和可维护性。 每一行的长度的限制是 80 列，我们强烈建议您遵守这个惯例。 -长于 80 列的语句要打散成有意义的片段。除非超过 80 列能显著增加可读性，并且不会隐藏 -信息。子片段要明显短于母片段，并明显靠右。这同样适用于有着很长参数列表的函数头。 -然而，绝对不要打散对用户可见的字符串，例如 printk 信息，因为这将导致无法 grep 这些 -信息。 +长于 80 列的语句要打散成有意义的片段。除非超过 80 列能显著增加可读性，并且不 +会隐藏信息。子片段要明显短于母片段，并明显靠右。这同样适用于有着很长参数列表 +的函数头。然而，绝对不要打散对用户可见的字符串，例如 printk 信息，因为这样就 +很难对它们 grep。 + - 第三章：大括号和空格的放置 +3) 大括号和空格的放置 +------------------------------ -C语言风格中另外一个常见问题是大括号的放置。和缩进大小不同，选择或弃用某种放置策 -略并没有多少技术上的原因，不过首选的方式，就像 Kernighan 和 Ritchie 展示给我们的， -是把起始大括号放在行尾，而把结束大括号放在行首，所以： +C 语言风格中另外一个常见问题是大括号的放置。和缩进大小不同，选择或弃用某种放 +置策略并没有多少技术上的原因，不过首选的方式，就像 Kernighan 和 Ritchie 展示 +给我们的，是把起始大括号放在行尾，而把结束大括号放在行首，所以： + +.. code-block:: c if (x is true) { we do y } -这适用于所有的非函数语句块（if、switch、for、while、do）。比如： +这适用于所有的非函数语句块 (if, switch, for, while, do)。比如： + +.. code-block:: c switch (action) { case KOBJ_ADD: @@ -118,17 +138,21 @@ C语言风格中另外一个常见问题是大括号的放置。和缩进大小 不过，有一个例外，那就是函数：函数的起始大括号放置于下一行的开头，所以： +.. code-block:: c + int function(int x) { body of function } -全世界的异端可能会抱怨这个不一致性是……呃……不一致的，不过所有思维健全的人都知道 -(a) K&R 是 _正确的_，并且 (b) K&R 是正确的。此外，不管怎样函数都是特殊的（C -函数是不能嵌套的）。 +全世界的异端可能会抱怨这个不一致性是... 呃... 不一致的，不过所有思维健全的人 +都知道 (a) K&R 是 **正确的** 并且 (b) K&R 是正确的。此外，不管怎样函数都是特 +殊的 (C 函数是不能嵌套的)。 + +注意结束大括号独自占据一行，除非它后面跟着同一个语句的剩余部分，也就是 do 语 +句中的 "while" 或者 if 语句中的 "else"，像这样： -注意结束大括号独自占据一行，除非它后面跟着同一个语句的剩余部分，也就是 do 语句中的 -“while” 或者 if 语句中的 “else”，像这样： +.. code-block:: c do { body of do-loop @@ -136,6 +160,8 @@ C语言风格中另外一个常见问题是大括号的放置。和缩进大小 和 +.. code-block:: c + if (x == y) { .. } else if (x > y) { @@ -146,17 +172,21 @@ C语言风格中另外一个常见问题是大括号的放置。和缩进大小 理由：K&R。 -也请注意这种大括号的放置方式也能使空（或者差不多空的）行的数量最小化，同时不失可 -读性。因此，由于你的屏幕上的新行是不可再生资源（想想 25 行的终端屏幕），你将会有更 -多的空行来放置注释。 +也请注意这种大括号的放置方式也能使空 (或者差不多空的) 行的数量最小化，同时不 +失可读性。因此，由于你的屏幕上的新行是不可再生资源 (想想 25 行的终端屏幕)，你 +将会有更多的空行来放置注释。 当只有一个单独的语句的时候，不用加不必要的大括号。 +.. code-block:: c + if (condition) action(); 和 +.. code-block:: c + if (condition) do_this(); else @@ -164,6 +194,8 @@ C语言风格中另外一个常见问题是大括号的放置。和缩进大小 这并不适用于只有一个条件分支是单语句的情况；这时所有分支都要使用大括号： +.. code-block:: c + if (condition) { do_this(); do_that(); @@ -171,88 +203,103 @@ C语言风格中另外一个常见问题是大括号的放置。和缩进大小 otherwise(); } - 3.1：空格 +3.1) 空格 +******************** -Linux 内核的空格使用方式（主要）取决于它是用于函数还是关键字。（大多数）关键字后 -要加一个空格。值得注意的例外是 sizeof、typeof、alignof 和 __attribute__，这些 -关键字某些程度上看起来更像函数（它们在 Linux 里也常常伴随小括号而使用，尽管在 C 里 -这样的小括号不是必需的，就像 “struct fileinfo info” 声明过后的 “sizeof info”）。 +Linux 内核的空格使用方式 (主要) 取决于它是用于函数还是关键字。(大多数) 关键字 +后要加一个空格。值得注意的例外是 sizeof, typeof, alignof 和 __attribute__，这 +些关键字某些程度上看起来更像函数 (它们在 Linux 里也常常伴随小括号而使用，尽管 +在 C 里这样的小括号不是必需的，就像 ``struct fileinfo info;`` 声明过后的 +``sizeof info``)。 -所以在这些关键字之后放一个空格： +所以在这些关键字之后放一个空格:: if, switch, case, for, do, while -但是不要在 sizeof、typeof、alignof 或者 __attribute__ 这些关键字之后放空格。例如， +但是不要在 sizeof, typeof, alignof 或者 __attribute__ 这些关键字之后放空格。 +例如， + +.. code-block:: c s = sizeof(struct file); -不要在小括号里的表达式两侧加空格。这是一个反例： +不要在小括号里的表达式两侧加空格。这是一个 **反例** ： + +.. code-block:: c s = sizeof( struct file ); -当声明指针类型或者返回指针类型的函数时，“*” 的首选使用方式是使之靠近变量名或者函 -数名，而不是靠近类型名。例子： +当声明指针类型或者返回指针类型的函数时， ``*`` 的首选使用方式是使之靠近变量名 +或者函数名，而不是靠近类型名。例子： + +.. code-block:: c char *linux_banner; unsigned long long memparse(char *ptr, char **retptr); char *match_strdup(substring_t *s); -在大多数二元和三元操作符两侧使用一个空格，例如下面所有这些操作符： +在大多数二元和三元操作符两侧使用一个空格，例如下面所有这些操作符:: = + - < > * / % | & ^ <= >= == != ? : -但是一元操作符后不要加空格： +但是一元操作符后不要加空格:: & * + - ~ ! sizeof typeof alignof __attribute__ defined -后缀自加和自减一元操作符前不加空格： +后缀自加和自减一元操作符前不加空格:: ++ -- -前缀自加和自减一元操作符后不加空格： +前缀自加和自减一元操作符后不加空格:: ++ -- -‘.’ 和 “->” 结构体成员操作符前后不加空格。 +``.`` 和 ``->`` 结构体成员操作符前后不加空格。 -不要在行尾留空白。有些可以自动缩进的编辑器会在新行的行首加入适量的空白，然后你 -就可以直接在那一行输入代码。不过假如你最后没有在那一行输入代码，有些编辑器就不 -会移除已经加入的空白，就像你故意留下一个只有空白的行。包含行尾空白的行就这样产 -生了。 +不要在行尾留空白。有些可以自动缩进的编辑器会在新行的行首加入适量的空白，然后 +你就可以直接在那一行输入代码。不过假如你最后没有在那一行输入代码，有些编辑器 +就不会移除已经加入的空白，就像你故意留下一个只有空白的行。包含行尾空白的行就 +这样产生了。 -当git发现补丁包含了行尾空白的时候会警告你，并且可以应你的要求去掉行尾空白；不过 -如果你是正在打一系列补丁，这样做会导致后面的补丁失败，因为你改变了补丁的上下文。 +当 git 发现补丁包含了行尾空白的时候会警告你，并且可以应你的要求去掉行尾空白； +不过如果你是正在打一系列补丁，这样做会导致后面的补丁失败，因为你改变了补丁的 +上下文。 - 第四章：命名 +4) 命名 +------------------------------ -C是一个简朴的语言，你的命名也应该这样。和 Modula-2 和 Pascal 程序员不同，C 程序员 -不使用类似 ThisVariableIsATemporaryCounter 这样华丽的名字。C 程序员会称那个变量 -为 “tmp”，这样写起来会更容易，而且至少不会令其难于理解。 +C 是一个简朴的语言，你的命名也应该这样。和 Modula-2 和 Pascal 程序员不同， +C 程序员不使用类似 ThisVariableIsATemporaryCounter 这样华丽的名字。C 程序员会 +称那个变量为 ``tmp`` ，这样写起来会更容易，而且至少不会令其难于理解。 -不过，虽然混用大小写的名字是不提倡使用的，但是全局变量还是需要一个具描述性的名字 -。称一个全局函数为 “foo” 是一个难以饶恕的错误。 +不过，虽然混用大小写的名字是不提倡使用的，但是全局变量还是需要一个具描述性的 +名字。称一个全局函数为 ``foo`` 是一个难以饶恕的错误。 -全局变量（只有当你真正需要它们的时候再用它）需要有一个具描述性的名字，就像全局函 -数。如果你有一个可以计算活动用户数量的函数，你应该叫它 “count_active_users()” -或者类似的名字，你不应该叫它 “cntuser()”。 +全局变量 (只有当你 **真正** 需要它们的时候再用它) 需要有一个具描述性的名字，就 +像全局函数。如果你有一个可以计算活动用户数量的函数，你应该叫它 +``count_active_users()`` 或者类似的名字，你不应该叫它 ``cntuser()`` 。 -在函数名中包含函数类型（所谓的匈牙利命名法）是脑子出了问题——编译器知道那些类型而 -且能够检查那些类型，这样做只能把程序员弄糊涂了。难怪微软总是制造出有问题的程序。 +在函数名中包含函数类型 (所谓的匈牙利命名法) 是脑子出了问题——编译器知道那些类 +型而且能够检查那些类型，这样做只能把程序员弄糊涂了。难怪微软总是制造出有问题 +的程序。 -本地变量名应该简短，而且能够表达相关的含义。如果你有一些随机的整数型的循环计数器 -，它应该被称为 “i”。叫它 “loop_counter” 并无益处，如果它没有被误解的可能的话。 -类似的，“tmp” 可以用来称呼任意类型的临时变量。 +本地变量名应该简短，而且能够表达相关的含义。如果你有一些随机的整数型的循环计 +数器，它应该被称为 ``i`` 。叫它 ``loop_counter`` 并无益处，如果它没有被误解的 +可能的话。类似的， ``tmp`` 可以用来称呼任意类型的临时变量。 -如果你怕混淆了你的本地变量名，你就遇到另一个问题了，叫做函数增长荷尔蒙失衡综合症 -。请看第六章（函数）。 +如果你怕混淆了你的本地变量名，你就遇到另一个问题了，叫做函数增长荷尔蒙失衡综 +合症。请看第六章 (函数)。 - 第五章：Typedef +5) Typedef +----------- -不要使用类似 “vps_t” 之类的东西。 +不要使用类似 ``vps_t`` 之类的东西。 -对结构体和指针使用 typedef 是一个错误。当你在代码里看到： +对结构体和指针使用 typedef 是一个 **错误** 。当你在代码里看到： + +.. code-block:: c vps_t a; @@ -260,75 +307,89 @@ C是一个简朴的语言，你的命名也应该这样。和 Modula-2 和 Pasca 相反，如果是这样 +.. code-block:: c + struct virtual_container *a; -你就知道 “a” 是什么了。 +你就知道 ``a`` 是什么了。 -很多人认为 typedef “能提高可读性”。实际不是这样的。它们只在下列情况下有用： +很多人认为 typedef ``能提高可读性`` 。实际不是这样的。它们只在下列情况下有用： - (a) 完全不透明的对象（这种情况下要主动使用 typedef 来隐藏这个对象实际上是什么）。 + (a) 完全不透明的对象 (这种情况下要主动使用 typedef 来 **隐藏** 这个对象实际上 + 是什么)。 - 例如：“pte_t” 等不透明对象，你只能用合适的访问函数来访问它们。 + 例如： ``pte_t`` 等不透明对象，你只能用合适的访问函数来访问它们。 - 注意！不透明性和“访问函数”本身是不好的。我们使用 pte_t 等类型的原因在于真的是 - 完全没有任何共用的可访问信息。 + .. note:: - (b) 清楚的整数类型，如此，这层抽象就可以帮助消除到底是 “int” 还是 “long” 的混淆。 + 不透明性和 "访问函数" 本身是不好的。我们使用 pte_t 等类型的原因在于真 + 的是完全没有任何共用的可访问信息。 + + (b) 清楚的整数类型，如此，这层抽象就可以 **帮助** 消除到底是 ``int`` 还是 + ``long`` 的混淆。 u8/u16/u32 是完全没有问题的 typedef，不过它们更符合类别 (d) 而不是这里。 - 再次注意！要这样做，必须事出有因。如果某个变量是 “unsigned long“，那么没有必要 + .. note:: + + 要这样做，必须事出有因。如果某个变量是 ``unsigned long`` ，那么没有必要 typedef unsigned long myflags_t; - 不过如果有一个明确的原因，比如它在某种情况下可能会是一个 “unsigned int” 而在 - 其他情况下可能为 “unsigned long”，那么就不要犹豫，请务必使用 typedef。 + 不过如果有一个明确的原因，比如它在某种情况下可能会是一个 ``unsigned int`` + 而在其他情况下可能为 ``unsigned long`` ，那么就不要犹豫，请务必使用 + typedef。 - (c) 当你使用sparse按字面的创建一个新类型来做类型检查的时候。 + (c) 当你使用 sparse 按字面的创建一个 **新** 类型来做类型检查的时候。 - (d) 和标准C99类型相同的类型，在某些例外的情况下。 + (d) 和标准 C99 类型相同的类型，在某些例外的情况下。 - 虽然让眼睛和脑筋来适应新的标准类型比如 “uint32_t” 不需要花很多时间，可是有些 - 人仍然拒绝使用它们。 + 虽然让眼睛和脑筋来适应新的标准类型比如 ``uint32_t`` 不需要花很多时间，可 + 是有些人仍然拒绝使用它们。 - 因此，Linux 特有的等同于标准类型的 “u8/u16/u32/u64” 类型和它们的有符号类型是被 - 允许的——尽管在你自己的新代码中，它们不是强制要求要使用的。 + 因此，Linux 特有的等同于标准类型的 ``u8/u16/u32/u64`` 类型和它们的有符号 + 类型是被允许的——尽管在你自己的新代码中，它们不是强制要求要使用的。 - 当编辑已经使用了某个类型集的已有代码时，你应该遵循那些代码中已经做出的选择。 + 当编辑已经使用了某个类型集的已有代码时，你应该遵循那些代码中已经做出的选 + 择。 (e) 可以在用户空间安全使用的类型。 - 在某些用户空间可见的结构体里，我们不能要求C99类型而且不能用上面提到的 “u32” - 类型。因此，我们在与用户空间共享的所有结构体中使用 __u32 和类似的类型。 + 在某些用户空间可见的结构体里，我们不能要求 C99 类型而且不能用上面提到的 + ``u32`` 类型。因此，我们在与用户空间共享的所有结构体中使用 __u32 和类似 + 的类型。 -可能还有其他的情况，不过基本的规则是永远不要使用 typedef，除非你可以明确的应用上 -述某个规则中的一个。 +可能还有其他的情况，不过基本的规则是 **永远不要** 使用 typedef，除非你可以明 +确的应用上述某个规则中的一个。 -总的来说，如果一个指针或者一个结构体里的元素可以合理的被直接访问到，那么它们就不 -应该是一个 typedef。 +总的来说，如果一个指针或者一个结构体里的元素可以合理的被直接访问到，那么它们 +就不应该是一个 typedef。 - 第六章：函数 +6) 函数 +------------------------------ -函数应该简短而漂亮，并且只完成一件事情。函数应该可以一屏或者两屏显示完（我们都知 -道 ISO/ANSI 屏幕大小是 80x24），只做一件事情，而且把它做好。 +函数应该简短而漂亮，并且只完成一件事情。函数应该可以一屏或者两屏显示完 (我们 +都知道 ISO/ANSI 屏幕大小是 80x24)，只做一件事情，而且把它做好。 -一个函数的最大长度是和该函数的复杂度和缩进级数成反比的。所以，如果你有一个理论上 -很简单的只有一个很长（但是简单）的 case 语句的函数，而且你需要在每个 case 里做 -很多很小的事情，这样的函数尽管很长，但也是可以的。 +一个函数的最大长度是和该函数的复杂度和缩进级数成反比的。所以，如果你有一个理 +论上很简单的只有一个很长 (但是简单) 的 case 语句的函数，而且你需要在每个 case +里做很多很小的事情，这样的函数尽管很长，但也是可以的。 -不过，如果你有一个复杂的函数，而且你怀疑一个天分不是很高的高中一年级学生可能甚至 -搞不清楚这个函数的目的，你应该严格的遵守前面提到的长度限制。使用辅助函数，并为之 -取个具描述性的名字（如果你觉得它们的性能很重要的话，可以让编译器内联它们，这样的 -效果往往会比你写一个复杂函数的效果要好。） +不过，如果你有一个复杂的函数，而且你怀疑一个天分不是很高的高中一年级学生可能 +甚至搞不清楚这个函数的目的，你应该严格遵守前面提到的长度限制。使用辅助函数， +并为之取个具描述性的名字 (如果你觉得它们的性能很重要的话，可以让编译器内联它 +们，这样的效果往往会比你写一个复杂函数的效果要好。) -函数的另外一个衡量标准是本地变量的数量。此数量不应超过 5－10 个，否则你的函数就有 -问题了。重新考虑一下你的函数，把它分拆成更小的函数。人的大脑一般可以轻松的同时跟 -踪 7 个不同的事物，如果再增多的话，就会糊涂了。即便你聪颖过人，你也可能会记不清你 -2 个星期前做过的事情。 +函数的另外一个衡量标准是本地变量的数量。此数量不应超过 5－10 个，否则你的函数 +就有问题了。重新考虑一下你的函数，把它分拆成更小的函数。人的大脑一般可以轻松 +的同时跟踪 7 个不同的事物，如果再增多的话，就会糊涂了。即便你聪颖过人，你也可 +能会记不清你 2 个星期前做过的事情。 -在源文件里，使用空行隔开不同的函数。如果该函数需要被导出，它的 EXPORT* 宏应该紧贴 -在它的结束大括号之下。比如： +在源文件里，使用空行隔开不同的函数。如果该函数需要被导出，它的 **EXPORT** 宏 +应该紧贴在它的结束大括号之下。比如： + +.. code-block:: c int system_is_up(void) { @@ -336,24 +397,32 @@ C是一个简朴的语言，你的命名也应该这样。和 Modula-2 和 Pasca } EXPORT_SYMBOL(system_is_up); -在函数原型中，包含函数名和它们的数据类型。虽然C语言里没有这样的要求，在 Linux 里这 -是提倡的做法，因为这样可以很简单的给读者提供更多的有价值的信息。 +在函数原型中，包含函数名和它们的数据类型。虽然 C 语言里没有这样的要求，在 +Linux 里这是提倡的做法，因为这样可以很简单的给读者提供更多的有价值的信息。 + +7) 集中的函数退出途径 +------------------------------ - 第七章：集中的函数退出途径 +虽然被某些人声称已经过时，但是 goto 语句的等价物还是经常被编译器所使用，具体 +形式是无条件跳转指令。 -虽然被某些人声称已经过时，但是 goto 语句的等价物还是经常被编译器所使用，具体形式是 -无条件跳转指令。 +当一个函数从多个位置退出，并且需要做一些类似清理的常见操作时，goto 语句就很方 +便了。如果并不需要清理操作，那么直接 return 即可。 -当一个函数从多个位置退出，并且需要做一些类似清理的常见操作时，goto 语句就很方便了。 -如果并不需要清理操作，那么直接 return 即可。 +选择一个能够说明 goto 行为或它为何存在的标签名。如果 goto 要释放 ``buffer``, +一个不错的名字可以是 ``out_free_buffer:`` 。别去使用像 ``err1:`` 和 ``err2:`` +这样的GW_BASIC 名称，因为一旦你添加或删除了 (函数的) 退出路径，你就必须对它们 +重新编号，这样会难以去检验正确性。 -理由是： +使用 goto 的理由是： - 无条件语句容易理解和跟踪 - 嵌套程度减小 -- 可以避免由于修改时忘记更新某个单独的退出点而导致的错误 -- 减轻了编译器的工作，无需删除冗余代码;) +- 可以避免由于修改时忘记更新个别的退出点而导致错误 +- 让编译器省去删除冗余代码的工作 ;) + +.. code-block:: c int fun(int a) { @@ -369,41 +438,55 @@ C是一个简朴的语言，你的命名也应该这样。和 Modula-2 和 Pasca ... } result = 1; - goto out_buffer; + goto out_free_buffer; } ... - out_buffer: + out_free_buffer: kfree(buffer); return result; } -一个需要注意的常见错误是“一个 err 错误”，就像这样： +一个需要注意的常见错误是 ``一个 err 错误`` ，就像这样： + +.. code-block:: c err: kfree(foo->bar); kfree(foo); return ret; -这段代码的错误是，在某些退出路径上 “foo” 是 NULL。通常情况下，通过把它分离成两个 -错误标签 “err_bar:” 和 “err_foo:” 来修复这个错误。 +这段代码的错误是，在某些退出路径上 ``foo`` 是 NULL。通常情况下，通过把它分离 +成两个错误标签 ``err_free_bar:`` 和 ``err_free_foo:`` 来修复这个错误： + +.. code-block:: c + + err_free_bar: + kfree(foo->bar); + err_free_foo: + kfree(foo); + return ret; + +理想情况下，你应该模拟错误来测试所有退出路径。 - 第八章：注释 -注释是好的，不过有过度注释的危险。永远不要在注释里解释你的代码是如何运作的：更好 -的做法是让别人一看你的代码就可以明白，解释写的很差的代码是浪费时间。 +8) 注释 +------------------------------ -一般的，你想要你的注释告诉别人你的代码做了什么，而不是怎么做的。也请你不要把注释 -放在一个函数体内部：如果函数复杂到你需要独立的注释其中的一部分，你很可能需要回到 -第六章看一看。你可以做一些小注释来注明或警告某些很聪明（或者槽糕）的做法，但不要 -加太多。你应该做的，是把注释放在函数的头部，告诉人们它做了什么，也可以加上它做这 -些事情的原因。 +注释是好的，不过有过度注释的危险。永远不要在注释里解释你的代码是如何运作的： +更好的做法是让别人一看你的代码就可以明白，解释写的很差的代码是浪费时间。 -当注释内核API函数时，请使用 kernel-doc 格式。请看 -Documentation/doc-guide/和scripts/kernel-doc 以获得详细信息。 +一般的，你想要你的注释告诉别人你的代码做了什么，而不是怎么做的。也请你不要把 +注释放在一个函数体内部：如果函数复杂到你需要独立的注释其中的一部分，你很可能 +需要回到第六章看一看。你可以做一些小注释来注明或警告某些很聪明 (或者槽糕) 的 +做法，但不要加太多。你应该做的，是把注释放在函数的头部，告诉人们它做了什么， +也可以加上它做这些事情的原因。 -Linux的注释风格是 C89 “/* ... */” 风格。不要使用 C99 风格 “// ...” 注释。 +当注释内核 API 函数时，请使用 kernel-doc 格式。请看 +Documentation/doc-guide/ 和 scripts/kernel-doc 以获得详细信息。 -长（多行）的首选注释风格是： +长 (多行) 注释的首选风格是： + +.. code-block:: c /* * This is the preferred style for multi-line @@ -414,7 +497,9 @@ Linux的注释风格是 C89 “/* ... */” 风格。不要使用 C99 风格 “ * with beginning and ending almost-blank lines. */ -对于在 net/ 和 drivers/net/ 的文件，首选的长（多行）注释风格有些不同。 +对于在 net/ 和 drivers/net/ 的文件，首选的长 (多行) 注释风格有些不同。 + +.. code-block:: c /* The preferred comment style for files in net/ and drivers/net * looks like this. @@ -423,72 +508,77 @@ Linux的注释风格是 C89 “/* ... */” 风格。不要使用 C99 风格 “ * but there is no initial almost-blank line. */ -注释数据也是很重要的，不管是基本类型还是衍生类型。为了方便实现这一点，每一行应只 -声明一个数据（不要使用逗号来一次声明多个数据）。这样你就有空间来为每个数据写一段 -小注释来解释它们的用途了。 - - - 第九章：你已经把事情弄糟了 - -这没什么，我们都是这样。可能你的使用了很长时间 Unix 的朋友已经告诉你 “GNU emacs” 能 -自动帮你格式化 C 源代码，而且你也注意到了，确实是这样，不过它所使用的默认值和我们 -想要的相去甚远（实际上，甚至比随机打的还要差——无数个猴子在 GNU emacs 里打字永远不 -会创造出一个好程序）（译注：请参考 Infinite Monkey Theorem） - -所以你要么放弃 GNU emacs，要么改变它让它使用更合理的设定。要采用后一个方案，你可 -以把下面这段粘贴到你的 .emacs 文件里。 - -(defun c-lineup-arglist-tabs-only (ignored) - "Line up argument lists by tabs, not spaces" - (let* ((anchor (c-langelem-pos c-syntactic-element)) - (column (c-langelem-2nd-pos c-syntactic-element)) - (offset (- (1+ column) anchor)) - (steps (floor offset c-basic-offset))) - (* (max steps 1) - c-basic-offset))) - -(add-hook 'c-mode-common-hook - (lambda () - ;; Add kernel style - (c-add-style - "linux-tabs-only" - '("linux" (c-offsets-alist - (arglist-cont-nonempty - c-lineup-gcc-asm-reg - c-lineup-arglist-tabs-only)))))) - -(add-hook 'c-mode-hook - (lambda () - (let ((filename (buffer-file-name))) - ;; Enable kernel mode for the appropriate files - (when (and filename - (string-match (expand-file-name "~/src/linux-trees") - filename)) - (setq indent-tabs-mode t) - (setq show-trailing-whitespace t) - (c-set-style "linux-tabs-only"))))) - -这会让 emacs 在 ~/src/linux-trees 目录下的 C 源文件获得更好的内核代码风格。 - -不过就算你尝试让 emacs 正确的格式化代码失败了，也并不意味着你失去了一切：还可以用 -“indent”。 - -不过，GNU indent 也有和 GNU emacs 一样有问题的设定，所以你需要给它一些命令选项。不 -过，这还不算太糟糕，因为就算是 GNU indent 的作者也认同 K&R 的权威性（GNU 的人并不是 -坏人，他们只是在这个问题上被严重的误导了），所以你只要给 indent 指定选项 “-kr -i8” -（代表 “K&R，8 个字符缩进”），或者使用 “scripts/Lindent”，这样就可以以最时髦的方式 -缩进源代码。 - -“indent” 有很多选项，特别是重新格式化注释的时候，你可能需要看一下它的手册页。不过 -记住：“indent” 不能修正坏的编程习惯。 - - - 第十章：Kconfig 配置文件 - -对于遍布源码树的所有 Kconfig* 配置文件来说，它们缩进方式与 C 代码相比有所不同。紧挨 -在 “config” 定义下面的行缩进一个制表符，帮助信息则再多缩进 2 个空格。比如： - -config AUDIT +注释数据也是很重要的，不管是基本类型还是衍生类型。为了方便实现这一点，每一行 +应只声明一个数据 (不要使用逗号来一次声明多个数据)。这样你就有空间来为每个数据 +写一段小注释来解释它们的用途了。 + + +9) 你已经把事情弄糟了 +------------------------------ + +这没什么，我们都是这样。可能你的使用了很长时间 Unix 的朋友已经告诉你 +``GNU emacs`` 能自动帮你格式化 C 源代码，而且你也注意到了，确实是这样，不过它 +所使用的默认值和我们想要的相去甚远 (实际上，甚至比随机打的还要差——无数个猴子 +在 GNU emacs 里打字永远不会创造出一个好程序) (译注：Infinite Monkey Theorem) + +所以你要么放弃 GNU emacs，要么改变它让它使用更合理的设定。要采用后一个方案， +你可以把下面这段粘贴到你的 .emacs 文件里。 + +.. code-block:: none + + (defun c-lineup-arglist-tabs-only (ignored) + "Line up argument lists by tabs, not spaces" + (let* ((anchor (c-langelem-pos c-syntactic-element)) + (column (c-langelem-2nd-pos c-syntactic-element)) + (offset (- (1+ column) anchor)) + (steps (floor offset c-basic-offset))) + (* (max steps 1) + c-basic-offset))) + + (add-hook 'c-mode-common-hook + (lambda () + ;; Add kernel style + (c-add-style + "linux-tabs-only" + '("linux" (c-offsets-alist + (arglist-cont-nonempty + c-lineup-gcc-asm-reg + c-lineup-arglist-tabs-only)))))) + + (add-hook 'c-mode-hook + (lambda () + (let ((filename (buffer-file-name))) + ;; Enable kernel mode for the appropriate files + (when (and filename + (string-match (expand-file-name "~/src/linux-trees") + filename)) + (setq indent-tabs-mode t) + (setq show-trailing-whitespace t) + (c-set-style "linux-tabs-only"))))) + +这会让 emacs 在 ``~/src/linux-trees`` 下的 C 源文件获得更好的内核代码风格。 + +不过就算你尝试让 emacs 正确的格式化代码失败了，也并不意味着你失去了一切：还可 +以用 ``indent`` 。 + +不过，GNU indent 也有和 GNU emacs 一样有问题的设定，所以你需要给它一些命令选 +项。不过，这还不算太糟糕，因为就算是 GNU indent 的作者也认同 K&R 的权威性 +(GNU 的人并不是坏人，他们只是在这个问题上被严重的误导了)，所以你只要给 indent +指定选项 ``-kr -i8`` (代表 ``K&R，8 字符缩进``)，或使用 ``scripts/Lindent`` +这样就可以以最时髦的方式缩进源代码。 + +``indent`` 有很多选项，特别是重新格式化注释的时候，你可能需要看一下它的手册。 +不过记住： ``indent`` 不能修正坏的编程习惯。 + + +10) Kconfig 配置文件 +------------------------------ + +对于遍布源码树的所有 Kconfig* 配置文件来说，它们缩进方式有所不同。紧挨着 +``config`` 定义的行，用一个制表符缩进，然而 help 信息的缩进则额外增加 2 个空 +格。举个例子:: + + config AUDIT bool "Auditing support" depends on NET help @@ -497,10 +587,10 @@ config AUDIT logging of avc messages output). Does not do system-call auditing without CONFIG_AUDITSYSCALL. -而那些危险的功能（比如某些文件系统的写支持）应该在它们的提示字符串里显著的声明这 -一点： +而那些危险的功能 (比如某些文件系统的写支持) 应该在它们的提示字符串里显著的声 +明这一点:: -config ADFS_FS_RW + config ADFS_FS_RW bool "ADFS write support (DANGEROUS)" depends on ADFS_FS ... @@ -508,34 +598,38 @@ config ADFS_FS_RW 要查看配置文件的完整文档，请看 Documentation/kbuild/kconfig-language.txt。 - 第十一章：数据结构 +11) 数据结构 +------------------------------ -如果一个数据结构，在创建和销毁它的单线执行环境之外可见，那么它必须要有一个引用计 -数器。内核里没有垃圾收集（并且内核之外的垃圾收集慢且效率低下），这意味着你绝对需 -要记录你对这种数据结构的使用情况。 +如果一个数据结构，在创建和销毁它的单线执行环境之外可见，那么它必须要有一个引 +用计数器。内核里没有垃圾收集 (并且内核之外的垃圾收集慢且效率低下)，这意味着你 +绝对需要记录你对这种数据结构的使用情况。 -引用计数意味着你能够避免上锁，并且允许多个用户并行访问这个数据结构——而不需要担心 -这个数据结构仅仅因为暂时不被使用就消失了，那些用户可能不过是沉睡了一阵或者做了一 -些其他事情而已。 +引用计数意味着你能够避免上锁，并且允许多个用户并行访问这个数据结构——而不需要 +担心这个数据结构仅仅因为暂时不被使用就消失了，那些用户可能不过是沉睡了一阵或 +者做了一些其他事情而已。 -注意上锁不能取代引用计数。上锁是为了保持数据结构的一致性，而引用计数是一个内存管 -理技巧。通常二者都需要，不要把两个搞混了。 +注意上锁 **不能** 取代引用计数。上锁是为了保持数据结构的一致性，而引用计数是一 +个内存管理技巧。通常二者都需要，不要把两个搞混了。 -很多数据结构实际上有2级引用计数，它们通常有不同“类”的用户。子类计数器统计子类用 -户的数量，每当子类计数器减至零时，全局计数器减一。 +很多数据结构实际上有 2 级引用计数，它们通常有不同 ``类`` 的用户。子类计数器统 +计子类用户的数量，每当子类计数器减至零时，全局计数器减一。 -这种“多级引用计数”的例子可以在内存管理（“struct mm_struct”：mm_users 和 mm_count） -和文件系统（“struct super_block”：s_count和s_active）中找到。 +这种 ``多级引用计数`` 的例子可以在内存管理 (``struct mm_struct``: mm_users 和 +mm_count)，和文件系统 (``struct super_block``: s_count 和 s_active) 中找到。 -记住：如果另一个执行线索可以找到你的数据结构，但是这个数据结构没有引用计数器，这 -里几乎肯定是一个 bug。 +记住：如果另一个执行线索可以找到你的数据结构，但这个数据结构没有引用计数器， +这里几乎肯定是一个 bug。 - 第十二章：宏，枚举和RTL +12) 宏，枚举和RTL +------------------------------ 用于定义常量的宏的名字及枚举里的标签需要大写。 -#define CONSTANT 0x12345 +.. code-block:: c + + #define CONSTANT 0x12345 在定义几个相关的常量时，最好用枚举。 @@ -545,6 +639,8 @@ config ADFS_FS_RW 含有多个语句的宏应该被包含在一个 do-while 代码块里： +.. code-block:: c + #define macrofun(a, b, c) \ do { \ if (a == 5) \ @@ -555,33 +651,41 @@ config ADFS_FS_RW 1) 影响控制流程的宏： +.. code-block:: c + #define FOO(x) \ do { \ if (blah(x) < 0) \ return -EBUGGERED; \ } while (0) -非常不好。它看起来像一个函数，不过却能导致“调用”它的函数退出；不要打乱读者大脑里 -的语法分析器。 +**非常** 不好。它看起来像一个函数，不过却能导致 ``调用`` 它的函数退出；不要打 +乱读者大脑里的语法分析器。 2) 依赖于一个固定名字的本地变量的宏： +.. code-block:: c + #define FOO(val) bar(index, val) -可能看起来像是个不错的东西，不过它非常容易把读代码的人搞糊涂，而且容易导致看起来 -不相关的改动带来错误。 +可能看起来像是个不错的东西，不过它非常容易把读代码的人搞糊涂，而且容易导致看起 +来不相关的改动带来错误。 + +3) 作为左值的带参数的宏： FOO(x) = y；如果有人把 FOO 变成一个内联函数的话，这 + 种用法就会出错了。 -3) 作为左值的带参数的宏： FOO(x) = y；如果有人把 FOO 变成一个内联函数的话，这种用 -法就会出错了。 +4) 忘记了优先级：使用表达式定义常量的宏必须将表达式置于一对小括号之内。带参数 + 的宏也要注意此类问题。 -4) 忘记了优先级：使用表达式定义常量的宏必须将表达式置于一对小括号之内。带参数的 -宏也要注意此类问题。 +.. code-block:: c #define CONSTANT 0x4000 #define CONSTEXP (CONSTANT | 3) 5) 在宏里定义类似函数的本地变量时命名冲突： +.. code-block:: c + #define FOO(x) \ ({ \ typeof(x) ret; \ @@ -591,133 +695,154 @@ config ADFS_FS_RW ret 是本地变量的通用名字 - __foo_ret 更不容易与一个已存在的变量冲突。 -cpp 手册对宏的讲解很详细。gcc internals 手册也详细讲解了 RTL（译注：register -transfer language），内核里的汇编语言经常用到它。 +cpp 手册对宏的讲解很详细。gcc internals 手册也详细讲解了 RTL，内核里的汇编语 +言经常用到它。 - 第十三章：打印内核消息 +13) 打印内核消息 +------------------------------ -内核开发者应该是受过良好教育的。请一定注意内核信息的拼写，以给人以好的印象。不要 -用不规范的单词比如 “dont”，而要用 “do not”或者 “don't”。保证这些信息简单、明了、 -无歧义。 +内核开发者应该是受过良好教育的。请一定注意内核信息的拼写，以给人以好的印象。 +不要用不规范的单词比如 ``dont``，而要用 ``do not`` 或者 ``don't`` 。保证这些信 +息简单明了,无歧义。 -内核信息不必以句号（译注：英文句号，即点）结束。 +内核信息不必以英文句号结束。 在小括号里打印数字 (%d) 没有任何价值，应该避免这样做。 - 里有一些驱动模型诊断宏，你应该使用它们，以确保信息对应于正确的 -设备和驱动，并且被标记了正确的消息级别。这些宏有：dev_err()，dev_warn()， -dev_info() 等等。对于那些不和某个特定设备相关连的信息， 定义了 -pr_notice()，pr_info()，pr_warn()，pr_err() 和其他。 + 里有一些驱动模型诊断宏，你应该使用它们，以确保信息对应于正确 +的设备和驱动，并且被标记了正确的消息级别。这些宏有：dev_err(), dev_warn(), +dev_info() 等等。对于那些不和某个特定设备相关连的信息， 定义 +了 pr_notice(), pr_info(), pr_warn(), pr_err() 和其他。 -写出好的调试信息可以是一个很大的挑战；一旦你写出后，这些信息在远程除错时能提供极大 -的帮助。然而打印调试信息的处理方式同打印非调试信息不同。其他 pr_XXX() 函数能无条件地 -打印，pr_debug() 却不；默认情况下它不会被编译，除非定义了 DEBUG 或设定了 -CONFIG_DYNAMIC_DEBUG。实际这同样是为了 dev_dbg()，一个相关约定是在一个已经开启了 -DEBUG 时，使用 VERBOSE_DEBUG 来添加 dev_vdbg()。 +写出好的调试信息可以是一个很大的挑战；一旦你写出后，这些信息在远程除错时能提 +供极大的帮助。然而打印调试信息的处理方式同打印非调试信息不同。其他 pr_XXX() +函数能无条件地打印，pr_debug() 却不；默认情况下它不会被编译，除非定义了 DEBUG +或设定了 CONFIG_DYNAMIC_DEBUG。实际这同样是为了 dev_dbg()，一个相关约定是在一 +个已经开启了 DEBUG 时，使用 VERBOSE_DEBUG 来添加 dev_vdbg()。 许多子系统拥有 Kconfig 调试选项来开启 -DDEBUG 在对应的 Makefile 里面；在其他 -情况下，特殊文件使用 #define DEBUG。当一条调试信息需要被无条件打印时，例如，如果 -已经包含一个调试相关的 #ifdef 条件，printk(KERN_DEBUG ...) 就可被使用。 +情况下，特殊文件使用 #define DEBUG。当一条调试信息需要被无条件打印时，例如， +如果已经包含一个调试相关的 #ifdef 条件，printk(KERN_DEBUG ...) 就可被使用。 - 第十四章：分配内存 +14) 分配内存 +------------------------------ 内核提供了下面的一般用途的内存分配函数： -kmalloc()，kzalloc()，kmalloc_array()，kcalloc()，vmalloc() 和 vzalloc()。 +kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc() 和 vzalloc()。 请参考 API 文档以获取有关它们的详细信息。 传递结构体大小的首选形式是这样的： +.. code-block:: c + p = kmalloc(sizeof(*p), ...); -另外一种传递方式中，sizeof 的操作数是结构体的名字，这样会降低可读性，并且可能会引 -入 bug。有可能指针变量类型被改变时，而对应的传递给内存分配函数的 sizeof 的结果不变。 +另外一种传递方式中，sizeof 的操作数是结构体的名字，这样会降低可读性，并且可能 +会引入 bug。有可能指针变量类型被改变时，而对应的传递给内存分配函数的 sizeof +的结果不变。 -强制转换一个 void 指针返回值是多余的。C 语言本身保证了从 void 指针到其他任何指针类型 -的转换是没有问题的。 +强制转换一个 void 指针返回值是多余的。C 语言本身保证了从 void 指针到其他任何 +指针类型的转换是没有问题的。 分配一个数组的首选形式是这样的： +.. code-block:: c + p = kmalloc_array(n, sizeof(...), ...); 分配一个零长数组的首选形式是这样的： +.. code-block:: c + p = kcalloc(n, sizeof(...), ...); 两种形式检查分配大小 n * sizeof(...) 的溢出，如果溢出返回 NULL。 - 第十五章：内联弊病 +15) 内联弊病 +------------------------------ -有一个常见的误解是内联函数是 gcc 提供的可以让代码运行更快的一个选项。虽然使用内联 -函数有时候是恰当的（比如作为一种替代宏的方式，请看第十二章），不过很多情况下不是 -这样。inline 关键字的过度使用会使内核变大，从而使整个系统运行速度变慢。因为大内核 -会占用更多的指令高速缓存（译注：一级缓存通常是指令缓存和数据缓存分开的）而且会导 -致 pagecache 的可用内存减少。想象一下，一次pagecache未命中就会导致一次磁盘寻址， -将耗时 5 毫秒。5 毫秒的时间内 CPU 能执行很多很多指令。 +有一个常见的误解是 ``内联`` 是 gcc 提供的可以让代码运行更快的一个选项。虽然使 +用内联函数有时候是恰当的 (比如作为一种替代宏的方式，请看第十二章)，不过很多情 +况下不是这样。inline 的过度使用会使内核变大，从而使整个系统运行速度变慢。 +因为体积大内核会占用更多的指令高速缓存，而且会导致 pagecache 的可用内存减少。 +想象一下，一次 pagecache 未命中就会导致一次磁盘寻址，将耗时 5 毫秒。5 毫秒的 +时间内 CPU 能执行很多很多指令。 -一个基本的原则是如果一个函数有 3 行以上，就不要把它变成内联函数。这个原则的一个例 -外是，如果你知道某个参数是一个编译时常量，而且因为这个常量你确定编译器在编译时能 -优化掉你的函数的大部分代码，那仍然可以给它加上 inline 关键字。kmalloc() 内联函数就 -是一个很好的例子。 +一个基本的原则是如果一个函数有 3 行以上，就不要把它变成内联函数。这个原则的一 +个例外是，如果你知道某个参数是一个编译时常量，而且因为这个常量你确定编译器在 +编译时能优化掉你的函数的大部分代码，那仍然可以给它加上 inline 关键字。 +kmalloc() 内联函数就是一个很好的例子。 -人们经常主张给 static 的而且只用了一次的函数加上 inline，如此不会有任何损失，因为没 -有什么好权衡的。虽然从技术上说这是正确的，但是实际上这种情况下即使不加 inline gcc -也可以自动使其内联。而且其他用户可能会要求移除 inline，由此而来的争论会抵消 inline -自身的潜在价值，得不偿失。 +人们经常主张给 static 的而且只用了一次的函数加上 inline，如此不会有任何损失， +因为没有什么好权衡的。虽然从技术上说这是正确的，但是实际上这种情况下即使不加 +inline gcc 也可以自动使其内联。而且其他用户可能会要求移除 inline，由此而来的 +争论会抵消 inline 自身的潜在价值，得不偿失。 - 第十六章：函数返回值及命名 +16) 函数返回值及命名 +------------------------------ -函数可以返回很多种不同类型的值，最常见的一种是表明函数执行成功或者失败的值。这样 -的一个值可以表示为一个错误代码整数（-Exxx＝失败，0＝成功）或者一个“成功”布尔值（ -0＝失败，非0＝成功）。 +函数可以返回多种不同类型的值，最常见的一种是表明函数执行成功或者失败的值。这样 +的一个值可以表示为一个错误代码整数 (-Exxx＝失败，0＝成功) 或者一个 ``成功`` +布尔值 (0＝失败，非0＝成功)。 -混合使用这两种表达方式是难于发现的 bug 的来源。如果 C 语言本身严格区分整形和布尔型变 -量，那么编译器就能够帮我们发现这些错误……不过 C 语言不区分。为了避免产生这种 bug，请 -遵循下面的惯例： +混合使用这两种表达方式是难于发现的 bug 的来源。如果 C 语言本身严格区分整形和 +布尔型变量，那么编译器就能够帮我们发现这些错误... 不过 C 语言不区分。为了避免 +产生这种 bug，请遵循下面的惯例:: - 如果函数的名字是一个动作或者强制性的命令，那么这个函数应该返回错误代码整 - 数。如果是一个判断，那么函数应该返回一个“成功”布尔值。 + 如果函数的名字是一个动作或者强制性的命令，那么这个函数应该返回错误代 + 码整数。如果是一个判断，那么函数应该返回一个 "成功" 布尔值。 -比如，“add work” 是一个命令，所以 add_work() 函数在成功时返回 0，在失败时返回 -EBUSY。 -类似的，因为 “PCI device present” 是一个判断，所以 pci_dev_present() 函数在成功找到 -一个匹配的设备时应该返回 1，如果找不到时应该返回 0。 +比如， ``add work`` 是一个命令，所以 add_work() 在成功时返回 0，在失败时返回 +-EBUSY。类似的，因为 ``PCI device present`` 是一个判断，所以 pci_dev_present() +在成功找到一个匹配的设备时应该返回 1，如果找不到时应该返回 0。 -所有导出（译注：EXPORT）的函数都必须遵守这个惯例，所有的公共函数也都应该如此。私 -有（static）函数不需要如此，但是我们也推荐这样做。 +所有 EXPORTed 函数都必须遵守这个惯例，所有的公共函数也都应该如此。私有 +(static) 函数不需要如此，但是我们也推荐这样做。 -返回值是实际计算结果而不是计算是否成功的标志的函数不受此惯例的限制。一般的，他们 -通过返回一些正常值范围之外的结果来表示出错。典型的例子是返回指针的函数，他们使用 -NULL 或者 ERR_PTR 机制来报告错误。 +返回值是实际计算结果而不是计算是否成功的标志的函数不受此惯例的限制。一般的， +他们通过返回一些正常值范围之外的结果来表示出错。典型的例子是返回指针的函数， +他们使用 NULL 或者 ERR_PTR 机制来报告错误。 - 第十七章：不要重新发明内核宏 +17) 不要重新发明内核宏 +------------------------------ -头文件 include/linux/kernel.h 包含了一些宏，你应该使用它们，而不要自己写一些它们的 -变种。比如，如果你需要计算一个数组的长度，使用这个宏 +头文件 include/linux/kernel.h 包含了一些宏，你应该使用它们，而不要自己写一些 +它们的变种。比如，如果你需要计算一个数组的长度，使用这个宏 + +.. code-block:: c #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 类似的，如果你要计算某结构体成员的大小，使用 +.. code-block:: c + #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f)) -还有可以做严格的类型检查的 min() 和 max() 宏，如果你需要可以使用它们。你可以自己看看 -那个头文件里还定义了什么你可以拿来用的东西，如果有定义的话，你就不应在你的代码里 -自己重新定义。 +还有可以做严格的类型检查的 min() 和 max() 宏，如果你需要可以使用它们。你可以 +自己看看那个头文件里还定义了什么你可以拿来用的东西，如果有定义的话，你就不应 +在你的代码里自己重新定义。 - 第十八章：编辑器模式行和其他需要罗嗦的事情 +18) 编辑器模式行和其他需要罗嗦的事情 +-------------------------------------------------- 有一些编辑器可以解释嵌入在源文件里的由一些特殊标记标明的配置信息。比如，emacs 能够解释被标记成这样的行： +.. code-block:: c + -*- mode: c -*- 或者这样的： +.. code-block:: c + /* Local Variables: compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c" @@ -726,14 +851,17 @@ NULL 或者 ERR_PTR 机制来报告错误。 Vim 能够解释这样的标记： +.. code-block:: c + /* vim:set sw=8 noet */ -不要在源代码中包含任何这样的内容。每个人都有他自己的编辑器配置，你的源文件不应 -该覆盖别人的配置。这包括有关缩进和模式配置的标记。人们可以使用他们自己定制的模 -式，或者使用其他可以产生正确的缩进的巧妙方法。 +不要在源代码中包含任何这样的内容。每个人都有他自己的编辑器配置，你的源文件不 +应该覆盖别人的配置。这包括有关缩进和模式配置的标记。人们可以使用他们自己定制 +的模式，或者使用其他可以产生正确的缩进的巧妙方法。 - 第十九章：内联汇编 +19) 内联汇编 +------------------------------ 在特定架构的代码中，你可能需要内联汇编与 CPU 和平台相关功能连接。需要这么做时 就不要犹豫。然而，当 C 可以完成工作时，不要平白无故地使用内联汇编。在可能的情 @@ -743,7 +871,7 @@ Vim 能够解释这样的标记： 地写下只有细微差异内联汇编。记住内联汇编可以使用 C 参数。 大型，有一定复杂度的汇编函数应该放在 .S 文件内，用相应的 C 原型定义在 C 头文 -件中。汇编函数的 C 原型应该使用 “asmlinkage”。 +件中。汇编函数的 C 原型应该使用 ``asmlinkage`` 。 你可能需要把汇编语句标记为 volatile，用来阻止 GCC 在没发现任何副作用后就把它 移除了。你不必总是这样做，尽管，这不必要的举动会限制优化。 @@ -752,12 +880,15 @@ Vim 能够解释这样的标记： 除了最后一条指令外，在每个指令结尾加上 \n\t，让汇编输出时可以正确地缩进下一条 指令： +.. code-block:: c + asm ("magic %reg1, #42\n\t" "more_magic %reg2, %reg3" : /* outputs */ : /* inputs */ : /* clobbers */); - 第二十章：条件编译 +20) 条件编译 +------------------------------ 只要可能，就不要在 .c 文件里面使用预处理条件 (#if, #ifdef)；这样做让代码更难 阅读并且更难去跟踪逻辑。替代方案是，在头文件中用预处理条件提供给那些 .c 文件 @@ -776,6 +907,8 @@ Vim 能够解释这样的标记： 在代码中，尽可能地使用 IS_ENABLED 宏来转化某个 Kconfig 标记为 C 的布尔 表达式，并在一般的 C 条件中使用它： +.. code-block:: c + if (IS_ENABLED(CONFIG_SOMETHING)) { ... } @@ -785,15 +918,18 @@ Vim 能够解释这样的标记： 确性 (语法，类型，符号引用，等等)。因此，如果条件不满足，代码块内的引用符号就 不存在时，你还是必须去用 #ifdef。 -在任何有意义的 #if 或 #ifdef 块的末尾 (超过几行的)，在 #endif 同一行的后面写 -下注解，注释这个条件表达式。例如： +在任何有意义的 #if 或 #ifdef 块的末尾 (超过几行的)，在 #endif 同一行的后面写下 +注解，注释这个条件表达式。例如： + +.. code-block:: c #ifdef CONFIG_SOMETHING ... #endif /* CONFIG_SOMETHING */ - 附录 I：参考 +附录 I) 参考 +------------------- The C Programming Language, 第二版 作者：Brian W. Kernighan 和 Denni M. Ritchie. @@ -808,7 +944,7 @@ ISBN 0-201-61586-X. GNU 手册 - 遵循 K&R 标准和此文本 - cpp, gcc, gcc internals and indent, 都可以从 http://www.gnu.org/manual/ 找到 -WG14是C语言的国际标准化工作组，URL: http://www.open-std.org/JTC1/SC22/WG14/ +WG14 是 C 语言的国际标准化工作组，URL: http://www.open-std.org/JTC1/SC22/WG14/ -Kernel process/coding-style.rst，作者 greg@kroah.com 发表于OLS 2002： +Kernel process/coding-style.rst，作者 greg@kroah.com 发表于 OLS 2002： http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/ -- cgit v1.2.3 From 2069889ff78cb00fa274818b03cec6d976b3187c Mon Sep 17 00:00:00 2001 From: Andy Deng Date: Wed, 25 Jan 2017 12:14:33 +0800 Subject: docs/zh_CN: Add coding-style into docs build system Tested by the command: make htmldocs During the compiling process, zh_CN/coding-style.rst has no errors and warnings generated, the generated html document has been checked. Signed-off-by: Andy Deng Signed-off-by: Jonathan Corbet --- Documentation/index.rst | 10 +- Documentation/translations/zh_CN/CodingStyle | 950 ---------------------- Documentation/translations/zh_CN/coding-style.rst | 950 ++++++++++++++++++++++ Documentation/translations/zh_CN/index.rst | 12 + 4 files changed, 971 insertions(+), 951 deletions(-) delete mode 100644 Documentation/translations/zh_CN/CodingStyle create mode 100644 Documentation/translations/zh_CN/coding-style.rst create mode 100644 Documentation/translations/zh_CN/index.rst (limited to 'Documentation') diff --git a/Documentation/index.rst b/Documentation/index.rst index cb5d77699c60..f6e641a54bbc 100644 --- a/Documentation/index.rst +++ b/Documentation/index.rst @@ -47,7 +47,7 @@ These books get into the details of how specific kernel subsystems work from the point of view of a kernel developer. Much of the information here is taken directly from the kernel source, with supplemental material added as needed (or at least as we managed to add it — probably *not* all that is -needed). +needed). .. toctree:: :maxdepth: 2 @@ -68,6 +68,14 @@ Korean translations translations/ko_KR/index +Chinese translations +-------------------- + +.. toctree:: + :maxdepth: 1 + + translations/zh_CN/index + Indices and tables ================== diff --git a/Documentation/translations/zh_CN/CodingStyle b/Documentation/translations/zh_CN/CodingStyle deleted file mode 100644 index 1466aa64b8b4..000000000000 --- a/Documentation/translations/zh_CN/CodingStyle +++ /dev/null @@ -1,950 +0,0 @@ -Chinese translated version of Documentation/process/coding-style.rst - -If you have any comment or update to the content, please post to LKML directly. -However, if you have problem communicating in English you can also ask the -Chinese maintainer for help. Contact the Chinese maintainer, if this -translation is outdated or there is problem with translation. - -Chinese maintainer: Zhang Le - ---------------------------------------------------------------------- - -Documentation/process/coding-style.rst 的中文翻译 - -如果想评论或更新本文的内容，请直接发信到LKML。如果你使用英文交流有困难的话， -也可以向中文版维护者求助。如果本翻译更新不及时或者翻译存在问题，请联系中文版 -维护者:: - - 中文版维护者： 张乐 Zhang Le - 中文版翻译者： 张乐 Zhang Le - 中文版校译者： 王聪 Wang Cong - wheelz - 管旭东 Xudong Guan - Li Zefan - Wang Chen - -以下为正文 - ---------------------------------------------------------------------- - -Linux 内核代码风格 -========================= - -这是一个简短的文档，描述了 linux 内核的首选代码风格。代码风格是因人而异的， -而且我不愿意把自己的观点强加给任何人，但这就像我去做任何事情都必须遵循的原则 -那样，我也希望在绝大多数事上保持这种的态度。请 (在写代码时) 至少考虑一下这里 -的代码风格。 - -首先，我建议你打印一份 GNU 代码规范，然后不要读。烧了它，这是一个具有重大象征 -性意义的动作。 - -不管怎样，现在我们开始： - - -1) 缩进 --------------- - -制表符是 8 个字符，所以缩进也是 8 个字符。有些异端运动试图将缩进变为 4 (甚至 -2！) 字符深，这几乎相当于尝试将圆周率的值定义为 3。 - -理由：缩进的全部意义就在于清楚的定义一个控制块起止于何处。尤其是当你盯着你的 -屏幕连续看了 20 小时之后，你将会发现大一点的缩进会使你更容易分辨缩进。 - -现在，有些人会抱怨 8 个字符的缩进会使代码向右边移动的太远，在 80 个字符的终端 -屏幕上就很难读这样的代码。这个问题的答案是，如果你需要 3 级以上的缩进，不管用 -何种方式你的代码已经有问题了，应该修正你的程序。 - -简而言之，8 个字符的缩进可以让代码更容易阅读，还有一个好处是当你的函数嵌套太 -深的时候可以给你警告。留心这个警告。 - -在 switch 语句中消除多级缩进的首选的方式是让 ``switch`` 和从属于它的 ``case`` -标签对齐于同一列，而不要 ``两次缩进`` ``case`` 标签。比如： - -.. code-block:: c - - switch (suffix) { - case 'G': - case 'g': - mem <<= 30; - break; - case 'M': - case 'm': - mem <<= 20; - break; - case 'K': - case 'k': - mem <<= 10; - /* fall through */ - default: - break; - } - -不要把多个语句放在一行里，除非你有什么东西要隐藏： - -.. code-block:: c - - if (condition) do_this; - do_something_everytime; - -也不要在一行里放多个赋值语句。内核代码风格超级简单。就是避免可能导致别人误读 -的表达式。 - -除了注释、文档和 Kconfig 之外，不要使用空格来缩进，前面的例子是例外，是有意为 -之。 - -选用一个好的编辑器，不要在行尾留空格。 - - -2) 把长的行和字符串打散 ------------------------------- - -代码风格的意义就在于使用平常使用的工具来维持代码的可读性和可维护性。 - -每一行的长度的限制是 80 列，我们强烈建议您遵守这个惯例。 - -长于 80 列的语句要打散成有意义的片段。除非超过 80 列能显著增加可读性，并且不 -会隐藏信息。子片段要明显短于母片段，并明显靠右。这同样适用于有着很长参数列表 -的函数头。然而，绝对不要打散对用户可见的字符串，例如 printk 信息，因为这样就 -很难对它们 grep。 - - -3) 大括号和空格的放置 ------------------------------- - -C 语言风格中另外一个常见问题是大括号的放置。和缩进大小不同，选择或弃用某种放 -置策略并没有多少技术上的原因，不过首选的方式，就像 Kernighan 和 Ritchie 展示 -给我们的，是把起始大括号放在行尾，而把结束大括号放在行首，所以： - -.. code-block:: c - - if (x is true) { - we do y - } - -这适用于所有的非函数语句块 (if, switch, for, while, do)。比如： - -.. code-block:: c - - switch (action) { - case KOBJ_ADD: - return "add"; - case KOBJ_REMOVE: - return "remove"; - case KOBJ_CHANGE: - return "change"; - default: - return NULL; - } - -不过，有一个例外，那就是函数：函数的起始大括号放置于下一行的开头，所以： - -.. code-block:: c - - int function(int x) - { - body of function - } - -全世界的异端可能会抱怨这个不一致性是... 呃... 不一致的，不过所有思维健全的人 -都知道 (a) K&R 是 **正确的** 并且 (b) K&R 是正确的。此外，不管怎样函数都是特 -殊的 (C 函数是不能嵌套的)。 - -注意结束大括号独自占据一行，除非它后面跟着同一个语句的剩余部分，也就是 do 语 -句中的 "while" 或者 if 语句中的 "else"，像这样： - -.. code-block:: c - - do { - body of do-loop - } while (condition); - -和 - -.. code-block:: c - - if (x == y) { - .. - } else if (x > y) { - ... - } else { - .... - } - -理由：K&R。 - -也请注意这种大括号的放置方式也能使空 (或者差不多空的) 行的数量最小化，同时不 -失可读性。因此，由于你的屏幕上的新行是不可再生资源 (想想 25 行的终端屏幕)，你 -将会有更多的空行来放置注释。 - -当只有一个单独的语句的时候，不用加不必要的大括号。 - -.. code-block:: c - - if (condition) - action(); - -和 - -.. code-block:: c - - if (condition) - do_this(); - else - do_that(); - -这并不适用于只有一个条件分支是单语句的情况；这时所有分支都要使用大括号： - -.. code-block:: c - - if (condition) { - do_this(); - do_that(); - } else { - otherwise(); - } - -3.1) 空格 -******************** - -Linux 内核的空格使用方式 (主要) 取决于它是用于函数还是关键字。(大多数) 关键字 -后要加一个空格。值得注意的例外是 sizeof, typeof, alignof 和 __attribute__，这 -些关键字某些程度上看起来更像函数 (它们在 Linux 里也常常伴随小括号而使用，尽管 -在 C 里这样的小括号不是必需的，就像 ``struct fileinfo info;`` 声明过后的 -``sizeof info``)。 - -所以在这些关键字之后放一个空格:: - - if, switch, case, for, do, while - -但是不要在 sizeof, typeof, alignof 或者 __attribute__ 这些关键字之后放空格。 -例如， - -.. code-block:: c - - s = sizeof(struct file); - -不要在小括号里的表达式两侧加空格。这是一个 **反例** ： - -.. code-block:: c - - s = sizeof( struct file ); - -当声明指针类型或者返回指针类型的函数时， ``*`` 的首选使用方式是使之靠近变量名 -或者函数名，而不是靠近类型名。例子： - -.. code-block:: c - - char *linux_banner; - unsigned long long memparse(char *ptr, char **retptr); - char *match_strdup(substring_t *s); - -在大多数二元和三元操作符两侧使用一个空格，例如下面所有这些操作符:: - - = + - < > * / % | & ^ <= >= == != ? : - -但是一元操作符后不要加空格:: - - & * + - ~ ! sizeof typeof alignof __attribute__ defined - -后缀自加和自减一元操作符前不加空格:: - - ++ -- - -前缀自加和自减一元操作符后不加空格:: - - ++ -- - -``.`` 和 ``->`` 结构体成员操作符前后不加空格。 - -不要在行尾留空白。有些可以自动缩进的编辑器会在新行的行首加入适量的空白，然后 -你就可以直接在那一行输入代码。不过假如你最后没有在那一行输入代码，有些编辑器 -就不会移除已经加入的空白，就像你故意留下一个只有空白的行。包含行尾空白的行就 -这样产生了。 - -当 git 发现补丁包含了行尾空白的时候会警告你，并且可以应你的要求去掉行尾空白； -不过如果你是正在打一系列补丁，这样做会导致后面的补丁失败，因为你改变了补丁的 -上下文。 - - -4) 命名 ------------------------------- - -C 是一个简朴的语言，你的命名也应该这样。和 Modula-2 和 Pascal 程序员不同， -C 程序员不使用类似 ThisVariableIsATemporaryCounter 这样华丽的名字。C 程序员会 -称那个变量为 ``tmp`` ，这样写起来会更容易，而且至少不会令其难于理解。 - -不过，虽然混用大小写的名字是不提倡使用的，但是全局变量还是需要一个具描述性的 -名字。称一个全局函数为 ``foo`` 是一个难以饶恕的错误。 - -全局变量 (只有当你 **真正** 需要它们的时候再用它) 需要有一个具描述性的名字，就 -像全局函数。如果你有一个可以计算活动用户数量的函数，你应该叫它 -``count_active_users()`` 或者类似的名字，你不应该叫它 ``cntuser()`` 。 - -在函数名中包含函数类型 (所谓的匈牙利命名法) 是脑子出了问题——编译器知道那些类 -型而且能够检查那些类型，这样做只能把程序员弄糊涂了。难怪微软总是制造出有问题 -的程序。 - -本地变量名应该简短，而且能够表达相关的含义。如果你有一些随机的整数型的循环计 -数器，它应该被称为 ``i`` 。叫它 ``loop_counter`` 并无益处，如果它没有被误解的 -可能的话。类似的， ``tmp`` 可以用来称呼任意类型的临时变量。 - -如果你怕混淆了你的本地变量名，你就遇到另一个问题了，叫做函数增长荷尔蒙失衡综 -合症。请看第六章 (函数)。 - - -5) Typedef ------------ - -不要使用类似 ``vps_t`` 之类的东西。 - -对结构体和指针使用 typedef 是一个 **错误** 。当你在代码里看到： - -.. code-block:: c - - vps_t a; - -这代表什么意思呢？ - -相反，如果是这样 - -.. code-block:: c - - struct virtual_container *a; - -你就知道 ``a`` 是什么了。 - -很多人认为 typedef ``能提高可读性`` 。实际不是这样的。它们只在下列情况下有用： - - (a) 完全不透明的对象 (这种情况下要主动使用 typedef 来 **隐藏** 这个对象实际上 - 是什么)。 - - 例如： ``pte_t`` 等不透明对象，你只能用合适的访问函数来访问它们。 - - .. note:: - - 不透明性和 "访问函数" 本身是不好的。我们使用 pte_t 等类型的原因在于真 - 的是完全没有任何共用的可访问信息。 - - (b) 清楚的整数类型，如此，这层抽象就可以 **帮助** 消除到底是 ``int`` 还是 - ``long`` 的混淆。 - - u8/u16/u32 是完全没有问题的 typedef，不过它们更符合类别 (d) 而不是这里。 - - .. note:: - - 要这样做，必须事出有因。如果某个变量是 ``unsigned long`` ，那么没有必要 - - typedef unsigned long myflags_t; - - 不过如果有一个明确的原因，比如它在某种情况下可能会是一个 ``unsigned int`` - 而在其他情况下可能为 ``unsigned long`` ，那么就不要犹豫，请务必使用 - typedef。 - - (c) 当你使用 sparse 按字面的创建一个 **新** 类型来做类型检查的时候。 - - (d) 和标准 C99 类型相同的类型，在某些例外的情况下。 - - 虽然让眼睛和脑筋来适应新的标准类型比如 ``uint32_t`` 不需要花很多时间，可 - 是有些人仍然拒绝使用它们。 - - 因此，Linux 特有的等同于标准类型的 ``u8/u16/u32/u64`` 类型和它们的有符号 - 类型是被允许的——尽管在你自己的新代码中，它们不是强制要求要使用的。 - - 当编辑已经使用了某个类型集的已有代码时，你应该遵循那些代码中已经做出的选 - 择。 - - (e) 可以在用户空间安全使用的类型。 - - 在某些用户空间可见的结构体里，我们不能要求 C99 类型而且不能用上面提到的 - ``u32`` 类型。因此，我们在与用户空间共享的所有结构体中使用 __u32 和类似 - 的类型。 - -可能还有其他的情况，不过基本的规则是 **永远不要** 使用 typedef，除非你可以明 -确的应用上述某个规则中的一个。 - -总的来说，如果一个指针或者一个结构体里的元素可以合理的被直接访问到，那么它们 -就不应该是一个 typedef。 - - -6) 函数 ------------------------------- - -函数应该简短而漂亮，并且只完成一件事情。函数应该可以一屏或者两屏显示完 (我们 -都知道 ISO/ANSI 屏幕大小是 80x24)，只做一件事情，而且把它做好。 - -一个函数的最大长度是和该函数的复杂度和缩进级数成反比的。所以，如果你有一个理 -论上很简单的只有一个很长 (但是简单) 的 case 语句的函数，而且你需要在每个 case -里做很多很小的事情，这样的函数尽管很长，但也是可以的。 - -不过，如果你有一个复杂的函数，而且你怀疑一个天分不是很高的高中一年级学生可能 -甚至搞不清楚这个函数的目的，你应该严格遵守前面提到的长度限制。使用辅助函数， -并为之取个具描述性的名字 (如果你觉得它们的性能很重要的话，可以让编译器内联它 -们，这样的效果往往会比你写一个复杂函数的效果要好。) - -函数的另外一个衡量标准是本地变量的数量。此数量不应超过 5－10 个，否则你的函数 -就有问题了。重新考虑一下你的函数，把它分拆成更小的函数。人的大脑一般可以轻松 -的同时跟踪 7 个不同的事物，如果再增多的话，就会糊涂了。即便你聪颖过人，你也可 -能会记不清你 2 个星期前做过的事情。 - -在源文件里，使用空行隔开不同的函数。如果该函数需要被导出，它的 **EXPORT** 宏 -应该紧贴在它的结束大括号之下。比如： - -.. code-block:: c - - int system_is_up(void) - { - return system_state == SYSTEM_RUNNING; - } - EXPORT_SYMBOL(system_is_up); - -在函数原型中，包含函数名和它们的数据类型。虽然 C 语言里没有这样的要求，在 -Linux 里这是提倡的做法，因为这样可以很简单的给读者提供更多的有价值的信息。 - - -7) 集中的函数退出途径 ------------------------------- - -虽然被某些人声称已经过时，但是 goto 语句的等价物还是经常被编译器所使用，具体 -形式是无条件跳转指令。 - -当一个函数从多个位置退出，并且需要做一些类似清理的常见操作时，goto 语句就很方 -便了。如果并不需要清理操作，那么直接 return 即可。 - -选择一个能够说明 goto 行为或它为何存在的标签名。如果 goto 要释放 ``buffer``, -一个不错的名字可以是 ``out_free_buffer:`` 。别去使用像 ``err1:`` 和 ``err2:`` -这样的GW_BASIC 名称，因为一旦你添加或删除了 (函数的) 退出路径，你就必须对它们 -重新编号，这样会难以去检验正确性。 - -使用 goto 的理由是： - -- 无条件语句容易理解和跟踪 -- 嵌套程度减小 -- 可以避免由于修改时忘记更新个别的退出点而导致错误 -- 让编译器省去删除冗余代码的工作 ;) - -.. code-block:: c - - int fun(int a) - { - int result = 0; - char *buffer; - - buffer = kmalloc(SIZE, GFP_KERNEL); - if (!buffer) - return -ENOMEM; - - if (condition1) { - while (loop1) { - ... - } - result = 1; - goto out_free_buffer; - } - ... - out_free_buffer: - kfree(buffer); - return result; - } - -一个需要注意的常见错误是 ``一个 err 错误`` ，就像这样： - -.. code-block:: c - - err: - kfree(foo->bar); - kfree(foo); - return ret; - -这段代码的错误是，在某些退出路径上 ``foo`` 是 NULL。通常情况下，通过把它分离 -成两个错误标签 ``err_free_bar:`` 和 ``err_free_foo:`` 来修复这个错误： - -.. code-block:: c - - err_free_bar: - kfree(foo->bar); - err_free_foo: - kfree(foo); - return ret; - -理想情况下，你应该模拟错误来测试所有退出路径。 - - -8) 注释 ------------------------------- - -注释是好的，不过有过度注释的危险。永远不要在注释里解释你的代码是如何运作的： -更好的做法是让别人一看你的代码就可以明白，解释写的很差的代码是浪费时间。 - -一般的，你想要你的注释告诉别人你的代码做了什么，而不是怎么做的。也请你不要把 -注释放在一个函数体内部：如果函数复杂到你需要独立的注释其中的一部分，你很可能 -需要回到第六章看一看。你可以做一些小注释来注明或警告某些很聪明 (或者槽糕) 的 -做法，但不要加太多。你应该做的，是把注释放在函数的头部，告诉人们它做了什么， -也可以加上它做这些事情的原因。 - -当注释内核 API 函数时，请使用 kernel-doc 格式。请看 -Documentation/doc-guide/ 和 scripts/kernel-doc 以获得详细信息。 - -长 (多行) 注释的首选风格是： - -.. code-block:: c - - /* - * This is the preferred style for multi-line - * comments in the Linux kernel source code. - * Please use it consistently. - * - * Description: A column of asterisks on the left side, - * with beginning and ending almost-blank lines. - */ - -对于在 net/ 和 drivers/net/ 的文件，首选的长 (多行) 注释风格有些不同。 - -.. code-block:: c - - /* The preferred comment style for files in net/ and drivers/net - * looks like this. - * - * It is nearly the same as the generally preferred comment style, - * but there is no initial almost-blank line. - */ - -注释数据也是很重要的，不管是基本类型还是衍生类型。为了方便实现这一点，每一行 -应只声明一个数据 (不要使用逗号来一次声明多个数据)。这样你就有空间来为每个数据 -写一段小注释来解释它们的用途了。 - - -9) 你已经把事情弄糟了 ------------------------------- - -这没什么，我们都是这样。可能你的使用了很长时间 Unix 的朋友已经告诉你 -``GNU emacs`` 能自动帮你格式化 C 源代码，而且你也注意到了，确实是这样，不过它 -所使用的默认值和我们想要的相去甚远 (实际上，甚至比随机打的还要差——无数个猴子 -在 GNU emacs 里打字永远不会创造出一个好程序) (译注：Infinite Monkey Theorem) - -所以你要么放弃 GNU emacs，要么改变它让它使用更合理的设定。要采用后一个方案， -你可以把下面这段粘贴到你的 .emacs 文件里。 - -.. code-block:: none - - (defun c-lineup-arglist-tabs-only (ignored) - "Line up argument lists by tabs, not spaces" - (let* ((anchor (c-langelem-pos c-syntactic-element)) - (column (c-langelem-2nd-pos c-syntactic-element)) - (offset (- (1+ column) anchor)) - (steps (floor offset c-basic-offset))) - (* (max steps 1) - c-basic-offset))) - - (add-hook 'c-mode-common-hook - (lambda () - ;; Add kernel style - (c-add-style - "linux-tabs-only" - '("linux" (c-offsets-alist - (arglist-cont-nonempty - c-lineup-gcc-asm-reg - c-lineup-arglist-tabs-only)))))) - - (add-hook 'c-mode-hook - (lambda () - (let ((filename (buffer-file-name))) - ;; Enable kernel mode for the appropriate files - (when (and filename - (string-match (expand-file-name "~/src/linux-trees") - filename)) - (setq indent-tabs-mode t) - (setq show-trailing-whitespace t) - (c-set-style "linux-tabs-only"))))) - -这会让 emacs 在 ``~/src/linux-trees`` 下的 C 源文件获得更好的内核代码风格。 - -不过就算你尝试让 emacs 正确的格式化代码失败了，也并不意味着你失去了一切：还可 -以用 ``indent`` 。 - -不过，GNU indent 也有和 GNU emacs 一样有问题的设定，所以你需要给它一些命令选 -项。不过，这还不算太糟糕，因为就算是 GNU indent 的作者也认同 K&R 的权威性 -(GNU 的人并不是坏人，他们只是在这个问题上被严重的误导了)，所以你只要给 indent -指定选项 ``-kr -i8`` (代表 ``K&R，8 字符缩进``)，或使用 ``scripts/Lindent`` -这样就可以以最时髦的方式缩进源代码。 - -``indent`` 有很多选项，特别是重新格式化注释的时候，你可能需要看一下它的手册。 -不过记住： ``indent`` 不能修正坏的编程习惯。 - - -10) Kconfig 配置文件 ------------------------------- - -对于遍布源码树的所有 Kconfig* 配置文件来说，它们缩进方式有所不同。紧挨着 -``config`` 定义的行，用一个制表符缩进，然而 help 信息的缩进则额外增加 2 个空 -格。举个例子:: - - config AUDIT - bool "Auditing support" - depends on NET - help - Enable auditing infrastructure that can be used with another - kernel subsystem, such as SELinux (which requires this for - logging of avc messages output). Does not do system-call - auditing without CONFIG_AUDITSYSCALL. - -而那些危险的功能 (比如某些文件系统的写支持) 应该在它们的提示字符串里显著的声 -明这一点:: - - config ADFS_FS_RW - bool "ADFS write support (DANGEROUS)" - depends on ADFS_FS - ... - -要查看配置文件的完整文档，请看 Documentation/kbuild/kconfig-language.txt。 - - -11) 数据结构 ------------------------------- - -如果一个数据结构，在创建和销毁它的单线执行环境之外可见，那么它必须要有一个引 -用计数器。内核里没有垃圾收集 (并且内核之外的垃圾收集慢且效率低下)，这意味着你 -绝对需要记录你对这种数据结构的使用情况。 - -引用计数意味着你能够避免上锁，并且允许多个用户并行访问这个数据结构——而不需要 -担心这个数据结构仅仅因为暂时不被使用就消失了，那些用户可能不过是沉睡了一阵或 -者做了一些其他事情而已。 - -注意上锁 **不能** 取代引用计数。上锁是为了保持数据结构的一致性，而引用计数是一 -个内存管理技巧。通常二者都需要，不要把两个搞混了。 - -很多数据结构实际上有 2 级引用计数，它们通常有不同 ``类`` 的用户。子类计数器统 -计子类用户的数量，每当子类计数器减至零时，全局计数器减一。 - -这种 ``多级引用计数`` 的例子可以在内存管理 (``struct mm_struct``: mm_users 和 -mm_count)，和文件系统 (``struct super_block``: s_count 和 s_active) 中找到。 - -记住：如果另一个执行线索可以找到你的数据结构，但这个数据结构没有引用计数器， -这里几乎肯定是一个 bug。 - - -12) 宏，枚举和RTL ------------------------------- - -用于定义常量的宏的名字及枚举里的标签需要大写。 - -.. code-block:: c - - #define CONSTANT 0x12345 - -在定义几个相关的常量时，最好用枚举。 - -宏的名字请用大写字母，不过形如函数的宏的名字可以用小写字母。 - -一般的，如果能写成内联函数就不要写成像函数的宏。 - -含有多个语句的宏应该被包含在一个 do-while 代码块里： - -.. code-block:: c - - #define macrofun(a, b, c) \ - do { \ - if (a == 5) \ - do_this(b, c); \ - } while (0) - -使用宏的时候应避免的事情： - -1) 影响控制流程的宏： - -.. code-block:: c - - #define FOO(x) \ - do { \ - if (blah(x) < 0) \ - return -EBUGGERED; \ - } while (0) - -**非常** 不好。它看起来像一个函数，不过却能导致 ``调用`` 它的函数退出；不要打 -乱读者大脑里的语法分析器。 - -2) 依赖于一个固定名字的本地变量的宏： - -.. code-block:: c - - #define FOO(val) bar(index, val) - -可能看起来像是个不错的东西，不过它非常容易把读代码的人搞糊涂，而且容易导致看起 -来不相关的改动带来错误。 - -3) 作为左值的带参数的宏： FOO(x) = y；如果有人把 FOO 变成一个内联函数的话，这 - 种用法就会出错了。 - -4) 忘记了优先级：使用表达式定义常量的宏必须将表达式置于一对小括号之内。带参数 - 的宏也要注意此类问题。 - -.. code-block:: c - - #define CONSTANT 0x4000 - #define CONSTEXP (CONSTANT | 3) - -5) 在宏里定义类似函数的本地变量时命名冲突： - -.. code-block:: c - - #define FOO(x) \ - ({ \ - typeof(x) ret; \ - ret = calc_ret(x); \ - (ret); \ - }) - -ret 是本地变量的通用名字 - __foo_ret 更不容易与一个已存在的变量冲突。 - -cpp 手册对宏的讲解很详细。gcc internals 手册也详细讲解了 RTL，内核里的汇编语 -言经常用到它。 - - -13) 打印内核消息 ------------------------------- - -内核开发者应该是受过良好教育的。请一定注意内核信息的拼写，以给人以好的印象。 -不要用不规范的单词比如 ``dont``，而要用 ``do not`` 或者 ``don't`` 。保证这些信 -息简单明了,无歧义。 - -内核信息不必以英文句号结束。 - -在小括号里打印数字 (%d) 没有任何价值，应该避免这样做。 - - 里有一些驱动模型诊断宏，你应该使用它们，以确保信息对应于正确 -的设备和驱动，并且被标记了正确的消息级别。这些宏有：dev_err(), dev_warn(), -dev_info() 等等。对于那些不和某个特定设备相关连的信息， 定义 -了 pr_notice(), pr_info(), pr_warn(), pr_err() 和其他。 - -写出好的调试信息可以是一个很大的挑战；一旦你写出后，这些信息在远程除错时能提 -供极大的帮助。然而打印调试信息的处理方式同打印非调试信息不同。其他 pr_XXX() -函数能无条件地打印，pr_debug() 却不；默认情况下它不会被编译，除非定义了 DEBUG -或设定了 CONFIG_DYNAMIC_DEBUG。实际这同样是为了 dev_dbg()，一个相关约定是在一 -个已经开启了 DEBUG 时，使用 VERBOSE_DEBUG 来添加 dev_vdbg()。 - -许多子系统拥有 Kconfig 调试选项来开启 -DDEBUG 在对应的 Makefile 里面；在其他 -情况下，特殊文件使用 #define DEBUG。当一条调试信息需要被无条件打印时，例如， -如果已经包含一个调试相关的 #ifdef 条件，printk(KERN_DEBUG ...) 就可被使用。 - - -14) 分配内存 ------------------------------- - -内核提供了下面的一般用途的内存分配函数： -kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc() 和 vzalloc()。 -请参考 API 文档以获取有关它们的详细信息。 - -传递结构体大小的首选形式是这样的： - -.. code-block:: c - - p = kmalloc(sizeof(*p), ...); - -另外一种传递方式中，sizeof 的操作数是结构体的名字，这样会降低可读性，并且可能 -会引入 bug。有可能指针变量类型被改变时，而对应的传递给内存分配函数的 sizeof -的结果不变。 - -强制转换一个 void 指针返回值是多余的。C 语言本身保证了从 void 指针到其他任何 -指针类型的转换是没有问题的。 - -分配一个数组的首选形式是这样的： - -.. code-block:: c - - p = kmalloc_array(n, sizeof(...), ...); - -分配一个零长数组的首选形式是这样的： - -.. code-block:: c - - p = kcalloc(n, sizeof(...), ...); - -两种形式检查分配大小 n * sizeof(...) 的溢出，如果溢出返回 NULL。 - - -15) 内联弊病 ------------------------------- - -有一个常见的误解是 ``内联`` 是 gcc 提供的可以让代码运行更快的一个选项。虽然使 -用内联函数有时候是恰当的 (比如作为一种替代宏的方式，请看第十二章)，不过很多情 -况下不是这样。inline 的过度使用会使内核变大，从而使整个系统运行速度变慢。 -因为体积大内核会占用更多的指令高速缓存，而且会导致 pagecache 的可用内存减少。 -想象一下，一次 pagecache 未命中就会导致一次磁盘寻址，将耗时 5 毫秒。5 毫秒的 -时间内 CPU 能执行很多很多指令。 - -一个基本的原则是如果一个函数有 3 行以上，就不要把它变成内联函数。这个原则的一 -个例外是，如果你知道某个参数是一个编译时常量，而且因为这个常量你确定编译器在 -编译时能优化掉你的函数的大部分代码，那仍然可以给它加上 inline 关键字。 -kmalloc() 内联函数就是一个很好的例子。 - -人们经常主张给 static 的而且只用了一次的函数加上 inline，如此不会有任何损失， -因为没有什么好权衡的。虽然从技术上说这是正确的，但是实际上这种情况下即使不加 -inline gcc 也可以自动使其内联。而且其他用户可能会要求移除 inline，由此而来的 -争论会抵消 inline 自身的潜在价值，得不偿失。 - - -16) 函数返回值及命名 ------------------------------- - -函数可以返回多种不同类型的值，最常见的一种是表明函数执行成功或者失败的值。这样 -的一个值可以表示为一个错误代码整数 (-Exxx＝失败，0＝成功) 或者一个 ``成功`` -布尔值 (0＝失败，非0＝成功)。 - -混合使用这两种表达方式是难于发现的 bug 的来源。如果 C 语言本身严格区分整形和 -布尔型变量，那么编译器就能够帮我们发现这些错误... 不过 C 语言不区分。为了避免 -产生这种 bug，请遵循下面的惯例:: - - 如果函数的名字是一个动作或者强制性的命令，那么这个函数应该返回错误代 - 码整数。如果是一个判断，那么函数应该返回一个 "成功" 布尔值。 - -比如， ``add work`` 是一个命令，所以 add_work() 在成功时返回 0，在失败时返回 --EBUSY。类似的，因为 ``PCI device present`` 是一个判断，所以 pci_dev_present() -在成功找到一个匹配的设备时应该返回 1，如果找不到时应该返回 0。 - -所有 EXPORTed 函数都必须遵守这个惯例，所有的公共函数也都应该如此。私有 -(static) 函数不需要如此，但是我们也推荐这样做。 - -返回值是实际计算结果而不是计算是否成功的标志的函数不受此惯例的限制。一般的， -他们通过返回一些正常值范围之外的结果来表示出错。典型的例子是返回指针的函数， -他们使用 NULL 或者 ERR_PTR 机制来报告错误。 - - -17) 不要重新发明内核宏 ------------------------------- - -头文件 include/linux/kernel.h 包含了一些宏，你应该使用它们，而不要自己写一些 -它们的变种。比如，如果你需要计算一个数组的长度，使用这个宏 - -.. code-block:: c - - #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) - -类似的，如果你要计算某结构体成员的大小，使用 - -.. code-block:: c - - #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f)) - -还有可以做严格的类型检查的 min() 和 max() 宏，如果你需要可以使用它们。你可以 -自己看看那个头文件里还定义了什么你可以拿来用的东西，如果有定义的话，你就不应 -在你的代码里自己重新定义。 - - -18) 编辑器模式行和其他需要罗嗦的事情 --------------------------------------------------- - -有一些编辑器可以解释嵌入在源文件里的由一些特殊标记标明的配置信息。比如，emacs -能够解释被标记成这样的行： - -.. code-block:: c - - -*- mode: c -*- - -或者这样的： - -.. code-block:: c - - /* - Local Variables: - compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c" - End: - */ - -Vim 能够解释这样的标记： - -.. code-block:: c - - /* vim:set sw=8 noet */ - -不要在源代码中包含任何这样的内容。每个人都有他自己的编辑器配置，你的源文件不 -应该覆盖别人的配置。这包括有关缩进和模式配置的标记。人们可以使用他们自己定制 -的模式，或者使用其他可以产生正确的缩进的巧妙方法。 - - -19) 内联汇编 ------------------------------- - -在特定架构的代码中，你可能需要内联汇编与 CPU 和平台相关功能连接。需要这么做时 -就不要犹豫。然而，当 C 可以完成工作时，不要平白无故地使用内联汇编。在可能的情 -况下，你可以并且应该用 C 和硬件沟通。 - -请考虑去写捆绑通用位元 (wrap common bits) 的内联汇编的简单辅助函数，别去重复 -地写下只有细微差异内联汇编。记住内联汇编可以使用 C 参数。 - -大型，有一定复杂度的汇编函数应该放在 .S 文件内，用相应的 C 原型定义在 C 头文 -件中。汇编函数的 C 原型应该使用 ``asmlinkage`` 。 - -你可能需要把汇编语句标记为 volatile，用来阻止 GCC 在没发现任何副作用后就把它 -移除了。你不必总是这样做，尽管，这不必要的举动会限制优化。 - -在写一个包含多条指令的单个内联汇编语句时，把每条指令用引号分割而且各占一行， -除了最后一条指令外，在每个指令结尾加上 \n\t，让汇编输出时可以正确地缩进下一条 -指令： - -.. code-block:: c - - asm ("magic %reg1, #42\n\t" - "more_magic %reg2, %reg3" - : /* outputs */ : /* inputs */ : /* clobbers */); - - -20) 条件编译 ------------------------------- - -只要可能，就不要在 .c 文件里面使用预处理条件 (#if, #ifdef)；这样做让代码更难 -阅读并且更难去跟踪逻辑。替代方案是，在头文件中用预处理条件提供给那些 .c 文件 -使用，再给 #else 提供一个空桩 (no-op stub) 版本，然后在 .c 文件内无条件地调用 -那些 (定义在头文件内的) 函数。这样做，编译器会避免为桩函数 (stub) 的调用生成 -任何代码，产生的结果是相同的，但逻辑将更加清晰。 - -最好倾向于编译整个函数，而不是函数的一部分或表达式的一部分。与其放一个 ifdef -在表达式内，不如分解出部分或全部表达式，放进一个单独的辅助函数，并应用预处理 -条件到这个辅助函数内。 - -如果你有一个在特定配置中，可能变成未使用的函数或变量，编译器会警告它定义了但 -未使用，把它标记为 __maybe_unused 而不是将它包含在一个预处理条件中。(然而，如 -果一个函数或变量总是未使用，就直接删除它。) - -在代码中，尽可能地使用 IS_ENABLED 宏来转化某个 Kconfig 标记为 C 的布尔 -表达式，并在一般的 C 条件中使用它： - -.. code-block:: c - - if (IS_ENABLED(CONFIG_SOMETHING)) { - ... - } - -编译器会做常量折叠，然后就像使用 #ifdef 那样去包含或排除代码块，所以这不会带 -来任何运行时开销。然而，这种方法依旧允许 C 编译器查看块内的代码，并检查它的正 -确性 (语法，类型，符号引用，等等)。因此，如果条件不满足，代码块内的引用符号就 -不存在时，你还是必须去用 #ifdef。 - -在任何有意义的 #if 或 #ifdef 块的末尾 (超过几行的)，在 #endif 同一行的后面写下 -注解，注释这个条件表达式。例如： - -.. code-block:: c - - #ifdef CONFIG_SOMETHING - ... - #endif /* CONFIG_SOMETHING */ - - -附录 I) 参考 -------------------- - -The C Programming Language, 第二版 -作者：Brian W. Kernighan 和 Denni M. Ritchie. -Prentice Hall, Inc., 1988. -ISBN 0-13-110362-8 (软皮), 0-13-110370-9 (硬皮). - -The Practice of Programming -作者：Brian W. Kernighan 和 Rob Pike. -Addison-Wesley, Inc., 1999. -ISBN 0-201-61586-X. - -GNU 手册 - 遵循 K&R 标准和此文本 - cpp, gcc, gcc internals and indent, -都可以从 http://www.gnu.org/manual/ 找到 - -WG14 是 C 语言的国际标准化工作组，URL: http://www.open-std.org/JTC1/SC22/WG14/ - -Kernel process/coding-style.rst，作者 greg@kroah.com 发表于 OLS 2002： -http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/ diff --git a/Documentation/translations/zh_CN/coding-style.rst b/Documentation/translations/zh_CN/coding-style.rst new file mode 100644 index 000000000000..1466aa64b8b4 --- /dev/null +++ b/Documentation/translations/zh_CN/coding-style.rst @@ -0,0 +1,950 @@ +Chinese translated version of Documentation/process/coding-style.rst + +If you have any comment or update to the content, please post to LKML directly. +However, if you have problem communicating in English you can also ask the +Chinese maintainer for help. Contact the Chinese maintainer, if this +translation is outdated or there is problem with translation. + +Chinese maintainer: Zhang Le + +--------------------------------------------------------------------- + +Documentation/process/coding-style.rst 的中文翻译 + +如果想评论或更新本文的内容，请直接发信到LKML。如果你使用英文交流有困难的话， +也可以向中文版维护者求助。如果本翻译更新不及时或者翻译存在问题，请联系中文版 +维护者:: + + 中文版维护者： 张乐 Zhang Le + 中文版翻译者： 张乐 Zhang Le + 中文版校译者： 王聪 Wang Cong + wheelz + 管旭东 Xudong Guan + Li Zefan + Wang Chen + +以下为正文 + +--------------------------------------------------------------------- + +Linux 内核代码风格 +========================= + +这是一个简短的文档，描述了 linux 内核的首选代码风格。代码风格是因人而异的， +而且我不愿意把自己的观点强加给任何人，但这就像我去做任何事情都必须遵循的原则 +那样，我也希望在绝大多数事上保持这种的态度。请 (在写代码时) 至少考虑一下这里 +的代码风格。 + +首先，我建议你打印一份 GNU 代码规范，然后不要读。烧了它，这是一个具有重大象征 +性意义的动作。 + +不管怎样，现在我们开始： + + +1) 缩进 +-------------- + +制表符是 8 个字符，所以缩进也是 8 个字符。有些异端运动试图将缩进变为 4 (甚至 +2！) 字符深，这几乎相当于尝试将圆周率的值定义为 3。 + +理由：缩进的全部意义就在于清楚的定义一个控制块起止于何处。尤其是当你盯着你的 +屏幕连续看了 20 小时之后，你将会发现大一点的缩进会使你更容易分辨缩进。 + +现在，有些人会抱怨 8 个字符的缩进会使代码向右边移动的太远，在 80 个字符的终端 +屏幕上就很难读这样的代码。这个问题的答案是，如果你需要 3 级以上的缩进，不管用 +何种方式你的代码已经有问题了，应该修正你的程序。 + +简而言之，8 个字符的缩进可以让代码更容易阅读，还有一个好处是当你的函数嵌套太 +深的时候可以给你警告。留心这个警告。 + +在 switch 语句中消除多级缩进的首选的方式是让 ``switch`` 和从属于它的 ``case`` +标签对齐于同一列，而不要 ``两次缩进`` ``case`` 标签。比如： + +.. code-block:: c + + switch (suffix) { + case 'G': + case 'g': + mem <<= 30; + break; + case 'M': + case 'm': + mem <<= 20; + break; + case 'K': + case 'k': + mem <<= 10; + /* fall through */ + default: + break; + } + +不要把多个语句放在一行里，除非你有什么东西要隐藏： + +.. code-block:: c + + if (condition) do_this; + do_something_everytime; + +也不要在一行里放多个赋值语句。内核代码风格超级简单。就是避免可能导致别人误读 +的表达式。 + +除了注释、文档和 Kconfig 之外，不要使用空格来缩进，前面的例子是例外，是有意为 +之。 + +选用一个好的编辑器，不要在行尾留空格。 + + +2) 把长的行和字符串打散 +------------------------------ + +代码风格的意义就在于使用平常使用的工具来维持代码的可读性和可维护性。 + +每一行的长度的限制是 80 列，我们强烈建议您遵守这个惯例。 + +长于 80 列的语句要打散成有意义的片段。除非超过 80 列能显著增加可读性，并且不 +会隐藏信息。子片段要明显短于母片段，并明显靠右。这同样适用于有着很长参数列表 +的函数头。然而，绝对不要打散对用户可见的字符串，例如 printk 信息，因为这样就 +很难对它们 grep。 + + +3) 大括号和空格的放置 +------------------------------ + +C 语言风格中另外一个常见问题是大括号的放置。和缩进大小不同，选择或弃用某种放 +置策略并没有多少技术上的原因，不过首选的方式，就像 Kernighan 和 Ritchie 展示 +给我们的，是把起始大括号放在行尾，而把结束大括号放在行首，所以： + +.. code-block:: c + + if (x is true) { + we do y + } + +这适用于所有的非函数语句块 (if, switch, for, while, do)。比如： + +.. code-block:: c + + switch (action) { + case KOBJ_ADD: + return "add"; + case KOBJ_REMOVE: + return "remove"; + case KOBJ_CHANGE: + return "change"; + default: + return NULL; + } + +不过，有一个例外，那就是函数：函数的起始大括号放置于下一行的开头，所以： + +.. code-block:: c + + int function(int x) + { + body of function + } + +全世界的异端可能会抱怨这个不一致性是... 呃... 不一致的，不过所有思维健全的人 +都知道 (a) K&R 是 **正确的** 并且 (b) K&R 是正确的。此外，不管怎样函数都是特 +殊的 (C 函数是不能嵌套的)。 + +注意结束大括号独自占据一行，除非它后面跟着同一个语句的剩余部分，也就是 do 语 +句中的 "while" 或者 if 语句中的 "else"，像这样： + +.. code-block:: c + + do { + body of do-loop + } while (condition); + +和 + +.. code-block:: c + + if (x == y) { + .. + } else if (x > y) { + ... + } else { + .... + } + +理由：K&R。 + +也请注意这种大括号的放置方式也能使空 (或者差不多空的) 行的数量最小化，同时不 +失可读性。因此，由于你的屏幕上的新行是不可再生资源 (想想 25 行的终端屏幕)，你 +将会有更多的空行来放置注释。 + +当只有一个单独的语句的时候，不用加不必要的大括号。 + +.. code-block:: c + + if (condition) + action(); + +和 + +.. code-block:: c + + if (condition) + do_this(); + else + do_that(); + +这并不适用于只有一个条件分支是单语句的情况；这时所有分支都要使用大括号： + +.. code-block:: c + + if (condition) { + do_this(); + do_that(); + } else { + otherwise(); + } + +3.1) 空格 +******************** + +Linux 内核的空格使用方式 (主要) 取决于它是用于函数还是关键字。(大多数) 关键字 +后要加一个空格。值得注意的例外是 sizeof, typeof, alignof 和 __attribute__，这 +些关键字某些程度上看起来更像函数 (它们在 Linux 里也常常伴随小括号而使用，尽管 +在 C 里这样的小括号不是必需的，就像 ``struct fileinfo info;`` 声明过后的 +``sizeof info``)。 + +所以在这些关键字之后放一个空格:: + + if, switch, case, for, do, while + +但是不要在 sizeof, typeof, alignof 或者 __attribute__ 这些关键字之后放空格。 +例如， + +.. code-block:: c + + s = sizeof(struct file); + +不要在小括号里的表达式两侧加空格。这是一个 **反例** ： + +.. code-block:: c + + s = sizeof( struct file ); + +当声明指针类型或者返回指针类型的函数时， ``*`` 的首选使用方式是使之靠近变量名 +或者函数名，而不是靠近类型名。例子： + +.. code-block:: c + + char *linux_banner; + unsigned long long memparse(char *ptr, char **retptr); + char *match_strdup(substring_t *s); + +在大多数二元和三元操作符两侧使用一个空格，例如下面所有这些操作符:: + + = + - < > * / % | & ^ <= >= == != ? : + +但是一元操作符后不要加空格:: + + & * + - ~ ! sizeof typeof alignof __attribute__ defined + +后缀自加和自减一元操作符前不加空格:: + + ++ -- + +前缀自加和自减一元操作符后不加空格:: + + ++ -- + +``.`` 和 ``->`` 结构体成员操作符前后不加空格。 + +不要在行尾留空白。有些可以自动缩进的编辑器会在新行的行首加入适量的空白，然后 +你就可以直接在那一行输入代码。不过假如你最后没有在那一行输入代码，有些编辑器 +就不会移除已经加入的空白，就像你故意留下一个只有空白的行。包含行尾空白的行就 +这样产生了。 + +当 git 发现补丁包含了行尾空白的时候会警告你，并且可以应你的要求去掉行尾空白； +不过如果你是正在打一系列补丁，这样做会导致后面的补丁失败，因为你改变了补丁的 +上下文。 + + +4) 命名 +------------------------------ + +C 是一个简朴的语言，你的命名也应该这样。和 Modula-2 和 Pascal 程序员不同， +C 程序员不使用类似 ThisVariableIsATemporaryCounter 这样华丽的名字。C 程序员会 +称那个变量为 ``tmp`` ，这样写起来会更容易，而且至少不会令其难于理解。 + +不过，虽然混用大小写的名字是不提倡使用的，但是全局变量还是需要一个具描述性的 +名字。称一个全局函数为 ``foo`` 是一个难以饶恕的错误。 + +全局变量 (只有当你 **真正** 需要它们的时候再用它) 需要有一个具描述性的名字，就 +像全局函数。如果你有一个可以计算活动用户数量的函数，你应该叫它 +``count_active_users()`` 或者类似的名字，你不应该叫它 ``cntuser()`` 。 + +在函数名中包含函数类型 (所谓的匈牙利命名法) 是脑子出了问题——编译器知道那些类 +型而且能够检查那些类型，这样做只能把程序员弄糊涂了。难怪微软总是制造出有问题 +的程序。 + +本地变量名应该简短，而且能够表达相关的含义。如果你有一些随机的整数型的循环计 +数器，它应该被称为 ``i`` 。叫它 ``loop_counter`` 并无益处，如果它没有被误解的 +可能的话。类似的， ``tmp`` 可以用来称呼任意类型的临时变量。 + +如果你怕混淆了你的本地变量名，你就遇到另一个问题了，叫做函数增长荷尔蒙失衡综 +合症。请看第六章 (函数)。 + + +5) Typedef +----------- + +不要使用类似 ``vps_t`` 之类的东西。 + +对结构体和指针使用 typedef 是一个 **错误** 。当你在代码里看到： + +.. code-block:: c + + vps_t a; + +这代表什么意思呢？ + +相反，如果是这样 + +.. code-block:: c + + struct virtual_container *a; + +你就知道 ``a`` 是什么了。 + +很多人认为 typedef ``能提高可读性`` 。实际不是这样的。它们只在下列情况下有用： + + (a) 完全不透明的对象 (这种情况下要主动使用 typedef 来 **隐藏** 这个对象实际上 + 是什么)。 + + 例如： ``pte_t`` 等不透明对象，你只能用合适的访问函数来访问它们。 + + .. note:: + + 不透明性和 "访问函数" 本身是不好的。我们使用 pte_t 等类型的原因在于真 + 的是完全没有任何共用的可访问信息。 + + (b) 清楚的整数类型，如此，这层抽象就可以 **帮助** 消除到底是 ``int`` 还是 + ``long`` 的混淆。 + + u8/u16/u32 是完全没有问题的 typedef，不过它们更符合类别 (d) 而不是这里。 + + .. note:: + + 要这样做，必须事出有因。如果某个变量是 ``unsigned long`` ，那么没有必要 + + typedef unsigned long myflags_t; + + 不过如果有一个明确的原因，比如它在某种情况下可能会是一个 ``unsigned int`` + 而在其他情况下可能为 ``unsigned long`` ，那么就不要犹豫，请务必使用 + typedef。 + + (c) 当你使用 sparse 按字面的创建一个 **新** 类型来做类型检查的时候。 + + (d) 和标准 C99 类型相同的类型，在某些例外的情况下。 + + 虽然让眼睛和脑筋来适应新的标准类型比如 ``uint32_t`` 不需要花很多时间，可 + 是有些人仍然拒绝使用它们。 + + 因此，Linux 特有的等同于标准类型的 ``u8/u16/u32/u64`` 类型和它们的有符号 + 类型是被允许的——尽管在你自己的新代码中，它们不是强制要求要使用的。 + + 当编辑已经使用了某个类型集的已有代码时，你应该遵循那些代码中已经做出的选 + 择。 + + (e) 可以在用户空间安全使用的类型。 + + 在某些用户空间可见的结构体里，我们不能要求 C99 类型而且不能用上面提到的 + ``u32`` 类型。因此，我们在与用户空间共享的所有结构体中使用 __u32 和类似 + 的类型。 + +可能还有其他的情况，不过基本的规则是 **永远不要** 使用 typedef，除非你可以明 +确的应用上述某个规则中的一个。 + +总的来说，如果一个指针或者一个结构体里的元素可以合理的被直接访问到，那么它们 +就不应该是一个 typedef。 + + +6) 函数 +------------------------------ + +函数应该简短而漂亮，并且只完成一件事情。函数应该可以一屏或者两屏显示完 (我们 +都知道 ISO/ANSI 屏幕大小是 80x24)，只做一件事情，而且把它做好。 + +一个函数的最大长度是和该函数的复杂度和缩进级数成反比的。所以，如果你有一个理 +论上很简单的只有一个很长 (但是简单) 的 case 语句的函数，而且你需要在每个 case +里做很多很小的事情，这样的函数尽管很长，但也是可以的。 + +不过，如果你有一个复杂的函数，而且你怀疑一个天分不是很高的高中一年级学生可能 +甚至搞不清楚这个函数的目的，你应该严格遵守前面提到的长度限制。使用辅助函数， +并为之取个具描述性的名字 (如果你觉得它们的性能很重要的话，可以让编译器内联它 +们，这样的效果往往会比你写一个复杂函数的效果要好。) + +函数的另外一个衡量标准是本地变量的数量。此数量不应超过 5－10 个，否则你的函数 +就有问题了。重新考虑一下你的函数，把它分拆成更小的函数。人的大脑一般可以轻松 +的同时跟踪 7 个不同的事物，如果再增多的话，就会糊涂了。即便你聪颖过人，你也可 +能会记不清你 2 个星期前做过的事情。 + +在源文件里，使用空行隔开不同的函数。如果该函数需要被导出，它的 **EXPORT** 宏 +应该紧贴在它的结束大括号之下。比如： + +.. code-block:: c + + int system_is_up(void) + { + return system_state == SYSTEM_RUNNING; + } + EXPORT_SYMBOL(system_is_up); + +在函数原型中，包含函数名和它们的数据类型。虽然 C 语言里没有这样的要求，在 +Linux 里这是提倡的做法，因为这样可以很简单的给读者提供更多的有价值的信息。 + + +7) 集中的函数退出途径 +------------------------------ + +虽然被某些人声称已经过时，但是 goto 语句的等价物还是经常被编译器所使用，具体 +形式是无条件跳转指令。 + +当一个函数从多个位置退出，并且需要做一些类似清理的常见操作时，goto 语句就很方 +便了。如果并不需要清理操作，那么直接 return 即可。 + +选择一个能够说明 goto 行为或它为何存在的标签名。如果 goto 要释放 ``buffer``, +一个不错的名字可以是 ``out_free_buffer:`` 。别去使用像 ``err1:`` 和 ``err2:`` +这样的GW_BASIC 名称，因为一旦你添加或删除了 (函数的) 退出路径，你就必须对它们 +重新编号，这样会难以去检验正确性。 + +使用 goto 的理由是： + +- 无条件语句容易理解和跟踪 +- 嵌套程度减小 +- 可以避免由于修改时忘记更新个别的退出点而导致错误 +- 让编译器省去删除冗余代码的工作 ;) + +.. code-block:: c + + int fun(int a) + { + int result = 0; + char *buffer; + + buffer = kmalloc(SIZE, GFP_KERNEL); + if (!buffer) + return -ENOMEM; + + if (condition1) { + while (loop1) { + ... + } + result = 1; + goto out_free_buffer; + } + ... + out_free_buffer: + kfree(buffer); + return result; + } + +一个需要注意的常见错误是 ``一个 err 错误`` ，就像这样： + +.. code-block:: c + + err: + kfree(foo->bar); + kfree(foo); + return ret; + +这段代码的错误是，在某些退出路径上 ``foo`` 是 NULL。通常情况下，通过把它分离 +成两个错误标签 ``err_free_bar:`` 和 ``err_free_foo:`` 来修复这个错误： + +.. code-block:: c + + err_free_bar: + kfree(foo->bar); + err_free_foo: + kfree(foo); + return ret; + +理想情况下，你应该模拟错误来测试所有退出路径。 + + +8) 注释 +------------------------------ + +注释是好的，不过有过度注释的危险。永远不要在注释里解释你的代码是如何运作的： +更好的做法是让别人一看你的代码就可以明白，解释写的很差的代码是浪费时间。 + +一般的，你想要你的注释告诉别人你的代码做了什么，而不是怎么做的。也请你不要把 +注释放在一个函数体内部：如果函数复杂到你需要独立的注释其中的一部分，你很可能 +需要回到第六章看一看。你可以做一些小注释来注明或警告某些很聪明 (或者槽糕) 的 +做法，但不要加太多。你应该做的，是把注释放在函数的头部，告诉人们它做了什么， +也可以加上它做这些事情的原因。 + +当注释内核 API 函数时，请使用 kernel-doc 格式。请看 +Documentation/doc-guide/ 和 scripts/kernel-doc 以获得详细信息。 + +长 (多行) 注释的首选风格是： + +.. code-block:: c + + /* + * This is the preferred style for multi-line + * comments in the Linux kernel source code. + * Please use it consistently. + * + * Description: A column of asterisks on the left side, + * with beginning and ending almost-blank lines. + */ + +对于在 net/ 和 drivers/net/ 的文件，首选的长 (多行) 注释风格有些不同。 + +.. code-block:: c + + /* The preferred comment style for files in net/ and drivers/net + * looks like this. + * + * It is nearly the same as the generally preferred comment style, + * but there is no initial almost-blank line. + */ + +注释数据也是很重要的，不管是基本类型还是衍生类型。为了方便实现这一点，每一行 +应只声明一个数据 (不要使用逗号来一次声明多个数据)。这样你就有空间来为每个数据 +写一段小注释来解释它们的用途了。 + + +9) 你已经把事情弄糟了 +------------------------------ + +这没什么，我们都是这样。可能你的使用了很长时间 Unix 的朋友已经告诉你 +``GNU emacs`` 能自动帮你格式化 C 源代码，而且你也注意到了，确实是这样，不过它 +所使用的默认值和我们想要的相去甚远 (实际上，甚至比随机打的还要差——无数个猴子 +在 GNU emacs 里打字永远不会创造出一个好程序) (译注：Infinite Monkey Theorem) + +所以你要么放弃 GNU emacs，要么改变它让它使用更合理的设定。要采用后一个方案， +你可以把下面这段粘贴到你的 .emacs 文件里。 + +.. code-block:: none + + (defun c-lineup-arglist-tabs-only (ignored) + "Line up argument lists by tabs, not spaces" + (let* ((anchor (c-langelem-pos c-syntactic-element)) + (column (c-langelem-2nd-pos c-syntactic-element)) + (offset (- (1+ column) anchor)) + (steps (floor offset c-basic-offset))) + (* (max steps 1) + c-basic-offset))) + + (add-hook 'c-mode-common-hook + (lambda () + ;; Add kernel style + (c-add-style + "linux-tabs-only" + '("linux" (c-offsets-alist + (arglist-cont-nonempty + c-lineup-gcc-asm-reg + c-lineup-arglist-tabs-only)))))) + + (add-hook 'c-mode-hook + (lambda () + (let ((filename (buffer-file-name))) + ;; Enable kernel mode for the appropriate files + (when (and filename + (string-match (expand-file-name "~/src/linux-trees") + filename)) + (setq indent-tabs-mode t) + (setq show-trailing-whitespace t) + (c-set-style "linux-tabs-only"))))) + +这会让 emacs 在 ``~/src/linux-trees`` 下的 C 源文件获得更好的内核代码风格。 + +不过就算你尝试让 emacs 正确的格式化代码失败了，也并不意味着你失去了一切：还可 +以用 ``indent`` 。 + +不过，GNU indent 也有和 GNU emacs 一样有问题的设定，所以你需要给它一些命令选 +项。不过，这还不算太糟糕，因为就算是 GNU indent 的作者也认同 K&R 的权威性 +(GNU 的人并不是坏人，他们只是在这个问题上被严重的误导了)，所以你只要给 indent +指定选项 ``-kr -i8`` (代表 ``K&R，8 字符缩进``)，或使用 ``scripts/Lindent`` +这样就可以以最时髦的方式缩进源代码。 + +``indent`` 有很多选项，特别是重新格式化注释的时候，你可能需要看一下它的手册。 +不过记住： ``indent`` 不能修正坏的编程习惯。 + + +10) Kconfig 配置文件 +------------------------------ + +对于遍布源码树的所有 Kconfig* 配置文件来说，它们缩进方式有所不同。紧挨着 +``config`` 定义的行，用一个制表符缩进，然而 help 信息的缩进则额外增加 2 个空 +格。举个例子:: + + config AUDIT + bool "Auditing support" + depends on NET + help + Enable auditing infrastructure that can be used with another + kernel subsystem, such as SELinux (which requires this for + logging of avc messages output). Does not do system-call + auditing without CONFIG_AUDITSYSCALL. + +而那些危险的功能 (比如某些文件系统的写支持) 应该在它们的提示字符串里显著的声 +明这一点:: + + config ADFS_FS_RW + bool "ADFS write support (DANGEROUS)" + depends on ADFS_FS + ... + +要查看配置文件的完整文档，请看 Documentation/kbuild/kconfig-language.txt。 + + +11) 数据结构 +------------------------------ + +如果一个数据结构，在创建和销毁它的单线执行环境之外可见，那么它必须要有一个引 +用计数器。内核里没有垃圾收集 (并且内核之外的垃圾收集慢且效率低下)，这意味着你 +绝对需要记录你对这种数据结构的使用情况。 + +引用计数意味着你能够避免上锁，并且允许多个用户并行访问这个数据结构——而不需要 +担心这个数据结构仅仅因为暂时不被使用就消失了，那些用户可能不过是沉睡了一阵或 +者做了一些其他事情而已。 + +注意上锁 **不能** 取代引用计数。上锁是为了保持数据结构的一致性，而引用计数是一 +个内存管理技巧。通常二者都需要，不要把两个搞混了。 + +很多数据结构实际上有 2 级引用计数，它们通常有不同 ``类`` 的用户。子类计数器统 +计子类用户的数量，每当子类计数器减至零时，全局计数器减一。 + +这种 ``多级引用计数`` 的例子可以在内存管理 (``struct mm_struct``: mm_users 和 +mm_count)，和文件系统 (``struct super_block``: s_count 和 s_active) 中找到。 + +记住：如果另一个执行线索可以找到你的数据结构，但这个数据结构没有引用计数器， +这里几乎肯定是一个 bug。 + + +12) 宏，枚举和RTL +------------------------------ + +用于定义常量的宏的名字及枚举里的标签需要大写。 + +.. code-block:: c + + #define CONSTANT 0x12345 + +在定义几个相关的常量时，最好用枚举。 + +宏的名字请用大写字母，不过形如函数的宏的名字可以用小写字母。 + +一般的，如果能写成内联函数就不要写成像函数的宏。 + +含有多个语句的宏应该被包含在一个 do-while 代码块里： + +.. code-block:: c + + #define macrofun(a, b, c) \ + do { \ + if (a == 5) \ + do_this(b, c); \ + } while (0) + +使用宏的时候应避免的事情： + +1) 影响控制流程的宏： + +.. code-block:: c + + #define FOO(x) \ + do { \ + if (blah(x) < 0) \ + return -EBUGGERED; \ + } while (0) + +**非常** 不好。它看起来像一个函数，不过却能导致 ``调用`` 它的函数退出；不要打 +乱读者大脑里的语法分析器。 + +2) 依赖于一个固定名字的本地变量的宏： + +.. code-block:: c + + #define FOO(val) bar(index, val) + +可能看起来像是个不错的东西，不过它非常容易把读代码的人搞糊涂，而且容易导致看起 +来不相关的改动带来错误。 + +3) 作为左值的带参数的宏： FOO(x) = y；如果有人把 FOO 变成一个内联函数的话，这 + 种用法就会出错了。 + +4) 忘记了优先级：使用表达式定义常量的宏必须将表达式置于一对小括号之内。带参数 + 的宏也要注意此类问题。 + +.. code-block:: c + + #define CONSTANT 0x4000 + #define CONSTEXP (CONSTANT | 3) + +5) 在宏里定义类似函数的本地变量时命名冲突： + +.. code-block:: c + + #define FOO(x) \ + ({ \ + typeof(x) ret; \ + ret = calc_ret(x); \ + (ret); \ + }) + +ret 是本地变量的通用名字 - __foo_ret 更不容易与一个已存在的变量冲突。 + +cpp 手册对宏的讲解很详细。gcc internals 手册也详细讲解了 RTL，内核里的汇编语 +言经常用到它。 + + +13) 打印内核消息 +------------------------------ + +内核开发者应该是受过良好教育的。请一定注意内核信息的拼写，以给人以好的印象。 +不要用不规范的单词比如 ``dont``，而要用 ``do not`` 或者 ``don't`` 。保证这些信 +息简单明了,无歧义。 + +内核信息不必以英文句号结束。 + +在小括号里打印数字 (%d) 没有任何价值，应该避免这样做。 + + 里有一些驱动模型诊断宏，你应该使用它们，以确保信息对应于正确 +的设备和驱动，并且被标记了正确的消息级别。这些宏有：dev_err(), dev_warn(), +dev_info() 等等。对于那些不和某个特定设备相关连的信息， 定义 +了 pr_notice(), pr_info(), pr_warn(), pr_err() 和其他。 + +写出好的调试信息可以是一个很大的挑战；一旦你写出后，这些信息在远程除错时能提 +供极大的帮助。然而打印调试信息的处理方式同打印非调试信息不同。其他 pr_XXX() +函数能无条件地打印，pr_debug() 却不；默认情况下它不会被编译，除非定义了 DEBUG +或设定了 CONFIG_DYNAMIC_DEBUG。实际这同样是为了 dev_dbg()，一个相关约定是在一 +个已经开启了 DEBUG 时，使用 VERBOSE_DEBUG 来添加 dev_vdbg()。 + +许多子系统拥有 Kconfig 调试选项来开启 -DDEBUG 在对应的 Makefile 里面；在其他 +情况下，特殊文件使用 #define DEBUG。当一条调试信息需要被无条件打印时，例如， +如果已经包含一个调试相关的 #ifdef 条件，printk(KERN_DEBUG ...) 就可被使用。 + + +14) 分配内存 +------------------------------ + +内核提供了下面的一般用途的内存分配函数： +kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc() 和 vzalloc()。 +请参考 API 文档以获取有关它们的详细信息。 + +传递结构体大小的首选形式是这样的： + +.. code-block:: c + + p = kmalloc(sizeof(*p), ...); + +另外一种传递方式中，sizeof 的操作数是结构体的名字，这样会降低可读性，并且可能 +会引入 bug。有可能指针变量类型被改变时，而对应的传递给内存分配函数的 sizeof +的结果不变。 + +强制转换一个 void 指针返回值是多余的。C 语言本身保证了从 void 指针到其他任何 +指针类型的转换是没有问题的。 + +分配一个数组的首选形式是这样的： + +.. code-block:: c + + p = kmalloc_array(n, sizeof(...), ...); + +分配一个零长数组的首选形式是这样的： + +.. code-block:: c + + p = kcalloc(n, sizeof(...), ...); + +两种形式检查分配大小 n * sizeof(...) 的溢出，如果溢出返回 NULL。 + + +15) 内联弊病 +------------------------------ + +有一个常见的误解是 ``内联`` 是 gcc 提供的可以让代码运行更快的一个选项。虽然使 +用内联函数有时候是恰当的 (比如作为一种替代宏的方式，请看第十二章)，不过很多情 +况下不是这样。inline 的过度使用会使内核变大，从而使整个系统运行速度变慢。 +因为体积大内核会占用更多的指令高速缓存，而且会导致 pagecache 的可用内存减少。 +想象一下，一次 pagecache 未命中就会导致一次磁盘寻址，将耗时 5 毫秒。5 毫秒的 +时间内 CPU 能执行很多很多指令。 + +一个基本的原则是如果一个函数有 3 行以上，就不要把它变成内联函数。这个原则的一 +个例外是，如果你知道某个参数是一个编译时常量，而且因为这个常量你确定编译器在 +编译时能优化掉你的函数的大部分代码，那仍然可以给它加上 inline 关键字。 +kmalloc() 内联函数就是一个很好的例子。 + +人们经常主张给 static 的而且只用了一次的函数加上 inline，如此不会有任何损失， +因为没有什么好权衡的。虽然从技术上说这是正确的，但是实际上这种情况下即使不加 +inline gcc 也可以自动使其内联。而且其他用户可能会要求移除 inline，由此而来的 +争论会抵消 inline 自身的潜在价值，得不偿失。 + + +16) 函数返回值及命名 +------------------------------ + +函数可以返回多种不同类型的值，最常见的一种是表明函数执行成功或者失败的值。这样 +的一个值可以表示为一个错误代码整数 (-Exxx＝失败，0＝成功) 或者一个 ``成功`` +布尔值 (0＝失败，非0＝成功)。 + +混合使用这两种表达方式是难于发现的 bug 的来源。如果 C 语言本身严格区分整形和 +布尔型变量，那么编译器就能够帮我们发现这些错误... 不过 C 语言不区分。为了避免 +产生这种 bug，请遵循下面的惯例:: + + 如果函数的名字是一个动作或者强制性的命令，那么这个函数应该返回错误代 + 码整数。如果是一个判断，那么函数应该返回一个 "成功" 布尔值。 + +比如， ``add work`` 是一个命令，所以 add_work() 在成功时返回 0，在失败时返回 +-EBUSY。类似的，因为 ``PCI device present`` 是一个判断，所以 pci_dev_present() +在成功找到一个匹配的设备时应该返回 1，如果找不到时应该返回 0。 + +所有 EXPORTed 函数都必须遵守这个惯例，所有的公共函数也都应该如此。私有 +(static) 函数不需要如此，但是我们也推荐这样做。 + +返回值是实际计算结果而不是计算是否成功的标志的函数不受此惯例的限制。一般的， +他们通过返回一些正常值范围之外的结果来表示出错。典型的例子是返回指针的函数， +他们使用 NULL 或者 ERR_PTR 机制来报告错误。 + + +17) 不要重新发明内核宏 +------------------------------ + +头文件 include/linux/kernel.h 包含了一些宏，你应该使用它们，而不要自己写一些 +它们的变种。比如，如果你需要计算一个数组的长度，使用这个宏 + +.. code-block:: c + + #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) + +类似的，如果你要计算某结构体成员的大小，使用 + +.. code-block:: c + + #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f)) + +还有可以做严格的类型检查的 min() 和 max() 宏，如果你需要可以使用它们。你可以 +自己看看那个头文件里还定义了什么你可以拿来用的东西，如果有定义的话，你就不应 +在你的代码里自己重新定义。 + + +18) 编辑器模式行和其他需要罗嗦的事情 +-------------------------------------------------- + +有一些编辑器可以解释嵌入在源文件里的由一些特殊标记标明的配置信息。比如，emacs +能够解释被标记成这样的行： + +.. code-block:: c + + -*- mode: c -*- + +或者这样的： + +.. code-block:: c + + /* + Local Variables: + compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c" + End: + */ + +Vim 能够解释这样的标记： + +.. code-block:: c + + /* vim:set sw=8 noet */ + +不要在源代码中包含任何这样的内容。每个人都有他自己的编辑器配置，你的源文件不 +应该覆盖别人的配置。这包括有关缩进和模式配置的标记。人们可以使用他们自己定制 +的模式，或者使用其他可以产生正确的缩进的巧妙方法。 + + +19) 内联汇编 +------------------------------ + +在特定架构的代码中，你可能需要内联汇编与 CPU 和平台相关功能连接。需要这么做时 +就不要犹豫。然而，当 C 可以完成工作时，不要平白无故地使用内联汇编。在可能的情 +况下，你可以并且应该用 C 和硬件沟通。 + +请考虑去写捆绑通用位元 (wrap common bits) 的内联汇编的简单辅助函数，别去重复 +地写下只有细微差异内联汇编。记住内联汇编可以使用 C 参数。 + +大型，有一定复杂度的汇编函数应该放在 .S 文件内，用相应的 C 原型定义在 C 头文 +件中。汇编函数的 C 原型应该使用 ``asmlinkage`` 。 + +你可能需要把汇编语句标记为 volatile，用来阻止 GCC 在没发现任何副作用后就把它 +移除了。你不必总是这样做，尽管，这不必要的举动会限制优化。 + +在写一个包含多条指令的单个内联汇编语句时，把每条指令用引号分割而且各占一行， +除了最后一条指令外，在每个指令结尾加上 \n\t，让汇编输出时可以正确地缩进下一条 +指令： + +.. code-block:: c + + asm ("magic %reg1, #42\n\t" + "more_magic %reg2, %reg3" + : /* outputs */ : /* inputs */ : /* clobbers */); + + +20) 条件编译 +------------------------------ + +只要可能，就不要在 .c 文件里面使用预处理条件 (#if, #ifdef)；这样做让代码更难 +阅读并且更难去跟踪逻辑。替代方案是，在头文件中用预处理条件提供给那些 .c 文件 +使用，再给 #else 提供一个空桩 (no-op stub) 版本，然后在 .c 文件内无条件地调用 +那些 (定义在头文件内的) 函数。这样做，编译器会避免为桩函数 (stub) 的调用生成 +任何代码，产生的结果是相同的，但逻辑将更加清晰。 + +最好倾向于编译整个函数，而不是函数的一部分或表达式的一部分。与其放一个 ifdef +在表达式内，不如分解出部分或全部表达式，放进一个单独的辅助函数，并应用预处理 +条件到这个辅助函数内。 + +如果你有一个在特定配置中，可能变成未使用的函数或变量，编译器会警告它定义了但 +未使用，把它标记为 __maybe_unused 而不是将它包含在一个预处理条件中。(然而，如 +果一个函数或变量总是未使用，就直接删除它。) + +在代码中，尽可能地使用 IS_ENABLED 宏来转化某个 Kconfig 标记为 C 的布尔 +表达式，并在一般的 C 条件中使用它： + +.. code-block:: c + + if (IS_ENABLED(CONFIG_SOMETHING)) { + ... + } + +编译器会做常量折叠，然后就像使用 #ifdef 那样去包含或排除代码块，所以这不会带 +来任何运行时开销。然而，这种方法依旧允许 C 编译器查看块内的代码，并检查它的正 +确性 (语法，类型，符号引用，等等)。因此，如果条件不满足，代码块内的引用符号就 +不存在时，你还是必须去用 #ifdef。 + +在任何有意义的 #if 或 #ifdef 块的末尾 (超过几行的)，在 #endif 同一行的后面写下 +注解，注释这个条件表达式。例如： + +.. code-block:: c + + #ifdef CONFIG_SOMETHING + ... + #endif /* CONFIG_SOMETHING */ + + +附录 I) 参考 +------------------- + +The C Programming Language, 第二版 +作者：Brian W. Kernighan 和 Denni M. Ritchie. +Prentice Hall, Inc., 1988. +ISBN 0-13-110362-8 (软皮), 0-13-110370-9 (硬皮). + +The Practice of Programming +作者：Brian W. Kernighan 和 Rob Pike. +Addison-Wesley, Inc., 1999. +ISBN 0-201-61586-X. + +GNU 手册 - 遵循 K&R 标准和此文本 - cpp, gcc, gcc internals and indent, +都可以从 http://www.gnu.org/manual/ 找到 + +WG14 是 C 语言的国际标准化工作组，URL: http://www.open-std.org/JTC1/SC22/WG14/ + +Kernel process/coding-style.rst，作者 greg@kroah.com 发表于 OLS 2002： +http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/ diff --git a/Documentation/translations/zh_CN/index.rst b/Documentation/translations/zh_CN/index.rst new file mode 100644 index 000000000000..75956d669962 --- /dev/null +++ b/Documentation/translations/zh_CN/index.rst @@ -0,0 +1,12 @@ +.. raw:: latex + + \renewcommand\thesection* + \renewcommand\thesubsection* + +Chinese translations +==================== + +.. toctree:: + :maxdepth: 1 + + coding-style -- cgit v1.2.3 From 8a8a602fdb834ffce9cf3e9f6021a86cdada78f0 Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Fri, 27 Jan 2017 15:43:01 -0700 Subject: docs: Convert the deviceio template to RST Convert deviceiobook.tmpl to RST and incorporate it into the driver API manual. Like the rest of our documentation, this one could use some work. There's no mention of ioremap() and friends, no mention of io_read*() and friends. But we have nice documentation for all those folks writing new drivers that do port I/O :). The :c:func: notation has been left off of all the read*/write* functions. There's no kerneldoc comments for them anyway, so those links will never be live, and writing a bunch of repetitive "read a byte from I/O memory" comments lacks appeal. Cc: Matthew Wilcox Cc: Alan Cox Signed-off-by: Jonathan Corbet --- Documentation/DocBook/deviceiobook.tmpl | 323 -------------------------------- Documentation/driver-api/device-io.rst | 201 ++++++++++++++++++++ Documentation/driver-api/index.rst | 1 + 3 files changed, 202 insertions(+), 323 deletions(-) delete mode 100644 Documentation/DocBook/deviceiobook.tmpl create mode 100644 Documentation/driver-api/device-io.rst (limited to 'Documentation') diff --git a/Documentation/DocBook/deviceiobook.tmpl b/Documentation/DocBook/deviceiobook.tmpl deleted file mode 100644 index 54199a0dcf9a..000000000000 --- a/Documentation/DocBook/deviceiobook.tmpl +++ /dev/null @@ -1,323 +0,0 @@ - - - - - - Bus-Independent Device Accesses - - - - Matthew - Wilcox - -
- matthew@wil.cx -
- - - - - - - Alan - Cox - -
- alan@lxorguk.ukuu.org.uk -
- - - - - - 2001 - Matthew Wilcox - - - - - This documentation is free software; you can redistribute - it and/or modify it under the terms of the GNU General Public - License as published by the Free Software Foundation; either - version 2 of the License, or (at your option) any later - version. - - - - This program is distributed in the hope that it will be - useful, but WITHOUT ANY WARRANTY; without even the implied - warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. - See the GNU General Public License for more details. - - - - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - - - - For more details see the file COPYING in the source - distribution of Linux. - - - - - - - - Introduction - - Linux provides an API which abstracts performing IO across all busses - and devices, allowing device drivers to be written independently of - bus type. - - - - - Known Bugs And Assumptions - - None. - - - - - Memory Mapped IO - - Getting Access to the Device - - The most widely supported form of IO is memory mapped IO. - That is, a part of the CPU's address space is interpreted - not as accesses to memory, but as accesses to a device. Some - architectures define devices to be at a fixed address, but most - have some method of discovering devices. The PCI bus walk is a - good example of such a scheme. This document does not cover how - to receive such an address, but assumes you are starting with one. - Physical addresses are of type unsigned long. - - - - This address should not be used directly. Instead, to get an - address suitable for passing to the accessor functions described - below, you should call ioremap. - An address suitable for accessing the device will be returned to you. - - - - After you've finished using the device (say, in your module's - exit routine), call iounmap in order to return - the address space to the kernel. Most architectures allocate new - address space each time you call ioremap, and - they can run out unless you call iounmap. - - - - - Accessing the device - - The part of the interface most used by drivers is reading and - writing memory-mapped registers on the device. Linux provides - interfaces to read and write 8-bit, 16-bit, 32-bit and 64-bit - quantities. Due to a historical accident, these are named byte, - word, long and quad accesses. Both read and write accesses are - supported; there is no prefetch support at this time. - - - - The functions are named readb, - readw, readl, - readq, readb_relaxed, - readw_relaxed, readl_relaxed, - readq_relaxed, writeb, - writew, writel and - writeq. - - - - Some devices (such as framebuffers) would like to use larger - transfers than 8 bytes at a time. For these devices, the - memcpy_toio, memcpy_fromio - and memset_io functions are provided. - Do not use memset or memcpy on IO addresses; they - are not guaranteed to copy data in order. - - - - The read and write functions are defined to be ordered. That is the - compiler is not permitted to reorder the I/O sequence. When the - ordering can be compiler optimised, you can use - __readb and friends to indicate the relaxed ordering. Use - this with care. - - - - While the basic functions are defined to be synchronous with respect - to each other and ordered with respect to each other the busses the - devices sit on may themselves have asynchronicity. In particular many - authors are burned by the fact that PCI bus writes are posted - asynchronously. A driver author must issue a read from the same - device to ensure that writes have occurred in the specific cases the - author cares. This kind of property cannot be hidden from driver - writers in the API. In some cases, the read used to flush the device - may be expected to fail (if the card is resetting, for example). In - that case, the read should be done from config space, which is - guaranteed to soft-fail if the card doesn't respond. - - - - The following is an example of flushing a write to a device when - the driver would like to ensure the write's effects are visible prior - to continuing execution. - - - -static inline void -qla1280_disable_intrs(struct scsi_qla_host *ha) -{ - struct device_reg *reg; - - reg = ha->iobase; - /* disable risc and host interrupts */ - WRT_REG_WORD(&reg->ictrl, 0); - /* - * The following read will ensure that the above write - * has been received by the device before we return from this - * function. - */ - RD_REG_WORD(&reg->ictrl); - ha->flags.ints_enabled = 0; -} - - - - In addition to write posting, on some large multiprocessing systems - (e.g. SGI Challenge, Origin and Altix machines) posted writes won't - be strongly ordered coming from different CPUs. Thus it's important - to properly protect parts of your driver that do memory-mapped writes - with locks and use the mmiowb to make sure they - arrive in the order intended. Issuing a regular readX - will also ensure write ordering, but should only be used - when the driver has to be sure that the write has actually arrived - at the device (not that it's simply ordered with respect to other - writes), since a full readX is a relatively - expensive operation. - - - - Generally, one should use mmiowb prior to - releasing a spinlock that protects regions using writeb - or similar functions that aren't surrounded by - readb calls, which will ensure ordering and flushing. The - following pseudocode illustrates what might occur if write ordering - isn't guaranteed via mmiowb or one of the - readX functions. - - - -CPU A: spin_lock_irqsave(&dev_lock, flags) -CPU A: ... -CPU A: writel(newval, ring_ptr); -CPU A: spin_unlock_irqrestore(&dev_lock, flags) - ... -CPU B: spin_lock_irqsave(&dev_lock, flags) -CPU B: writel(newval2, ring_ptr); -CPU B: ... -CPU B: spin_unlock_irqrestore(&dev_lock, flags) - - - - In the case above, newval2 could be written to ring_ptr before - newval. Fixing it is easy though: - - - -CPU A: spin_lock_irqsave(&dev_lock, flags) -CPU A: ... -CPU A: writel(newval, ring_ptr); -CPU A: mmiowb(); /* ensure no other writes beat us to the device */ -CPU A: spin_unlock_irqrestore(&dev_lock, flags) - ... -CPU B: spin_lock_irqsave(&dev_lock, flags) -CPU B: writel(newval2, ring_ptr); -CPU B: ... -CPU B: mmiowb(); -CPU B: spin_unlock_irqrestore(&dev_lock, flags) - - - - See tg3.c for a real world example of how to use mmiowb - - - - - PCI ordering rules also guarantee that PIO read responses arrive - after any outstanding DMA writes from that bus, since for some devices - the result of a readb call may signal to the - driver that a DMA transaction is complete. In many cases, however, - the driver may want to indicate that the next - readb call has no relation to any previous DMA - writes performed by the device. The driver can use - readb_relaxed for these cases, although only - some platforms will honor the relaxed semantics. Using the relaxed - read functions will provide significant performance benefits on - platforms that support it. The qla2xxx driver provides examples - of how to use readX_relaxed. In many cases, - a majority of the driver's readX calls can - safely be converted to readX_relaxed calls, since - only a few will indicate or depend on DMA completion. - - - - - - - Port Space Accesses - - Port Space Explained - - - Another form of IO commonly supported is Port Space. This is a - range of addresses separate to the normal memory address space. - Access to these addresses is generally not as fast as accesses - to the memory mapped addresses, and it also has a potentially - smaller address space. - - - - Unlike memory mapped IO, no preparation is required - to access port space. - - - - - Accessing Port Space - - Accesses to this space are provided through a set of functions - which allow 8-bit, 16-bit and 32-bit accesses; also - known as byte, word and long. These functions are - inb, inw, - inl, outb, - outw and outl. - - - - Some variants are provided for these functions. Some devices - require that accesses to their ports are slowed down. This - functionality is provided by appending a _p - to the end of the function. There are also equivalents to memcpy. - The ins and outs - functions copy bytes, words or longs to the given port. - - - - - - - Public Functions Provided -!Iarch/x86/include/asm/io.h -!Elib/pci_iomap.c - - - diff --git a/Documentation/driver-api/device-io.rst b/Documentation/driver-api/device-io.rst new file mode 100644 index 000000000000..b00b23903078 --- /dev/null +++ b/Documentation/driver-api/device-io.rst @@ -0,0 +1,201 @@ +.. Copyright 2001 Matthew Wilcox +.. +.. This documentation is free software; you can redistribute +.. it and/or modify it under the terms of the GNU General Public +.. License as published by the Free Software Foundation; either +.. version 2 of the License, or (at your option) any later +.. version. + +=============================== +Bus-Independent Device Accesses +=============================== + +:Author: Matthew Wilcox +:Author: Alan Cox + +Introduction +============ + +Linux provides an API which abstracts performing IO across all busses +and devices, allowing device drivers to be written independently of bus +type. + +Memory Mapped IO +================ + +Getting Access to the Device +---------------------------- + +The most widely supported form of IO is memory mapped IO. That is, a +part of the CPU's address space is interpreted not as accesses to +memory, but as accesses to a device. Some architectures define devices +to be at a fixed address, but most have some method of discovering +devices. The PCI bus walk is a good example of such a scheme. This +document does not cover how to receive such an address, but assumes you +are starting with one. Physical addresses are of type unsigned long. + +This address should not be used directly. Instead, to get an address +suitable for passing to the accessor functions described below, you +should call :c:func:`ioremap()`. An address suitable for accessing +the device will be returned to you. + +After you've finished using the device (say, in your module's exit +routine), call :c:func:`iounmap()` in order to return the address +space to the kernel. Most architectures allocate new address space each +time you call :c:func:`ioremap()`, and they can run out unless you +call :c:func:`iounmap()`. + +Accessing the device +-------------------- + +The part of the interface most used by drivers is reading and writing +memory-mapped registers on the device. Linux provides interfaces to read +and write 8-bit, 16-bit, 32-bit and 64-bit quantities. Due to a +historical accident, these are named byte, word, long and quad accesses. +Both read and write accesses are supported; there is no prefetch support +at this time. + +The functions are named readb(), readw(), readl(), readq(), +readb_relaxed(), readw_relaxed(), readl_relaxed(), readq_relaxed(), +writeb(), writew(), writel() and writeq(). + +Some devices (such as framebuffers) would like to use larger transfers than +8 bytes at a time. For these devices, the :c:func:`memcpy_toio()`, +:c:func:`memcpy_fromio()` and :c:func:`memset_io()` functions are +provided. Do not use memset or memcpy on IO addresses; they are not +guaranteed to copy data in order. + +The read and write functions are defined to be ordered. That is the +compiler is not permitted to reorder the I/O sequence. When the ordering +can be compiler optimised, you can use __readb() and friends to +indicate the relaxed ordering. Use this with care. + +While the basic functions are defined to be synchronous with respect to +each other and ordered with respect to each other the busses the devices +sit on may themselves have asynchronicity. In particular many authors +are burned by the fact that PCI bus writes are posted asynchronously. A +driver author must issue a read from the same device to ensure that +writes have occurred in the specific cases the author cares. This kind +of property cannot be hidden from driver writers in the API. In some +cases, the read used to flush the device may be expected to fail (if the +card is resetting, for example). In that case, the read should be done +from config space, which is guaranteed to soft-fail if the card doesn't +respond. + +The following is an example of flushing a write to a device when the +driver would like to ensure the write's effects are visible prior to +continuing execution:: + + static inline void + qla1280_disable_intrs(struct scsi_qla_host *ha) + { + struct device_reg *reg; + + reg = ha->iobase; + /* disable risc and host interrupts */ + WRT_REG_WORD(®->ictrl, 0); + /* + * The following read will ensure that the above write + * has been received by the device before we return from this + * function. + */ + RD_REG_WORD(®->ictrl); + ha->flags.ints_enabled = 0; + } + +In addition to write posting, on some large multiprocessing systems +(e.g. SGI Challenge, Origin and Altix machines) posted writes won't be +strongly ordered coming from different CPUs. Thus it's important to +properly protect parts of your driver that do memory-mapped writes with +locks and use the :c:func:`mmiowb()` to make sure they arrive in the +order intended. Issuing a regular readX() will also ensure write ordering, +but should only be used when the +driver has to be sure that the write has actually arrived at the device +(not that it's simply ordered with respect to other writes), since a +full readX() is a relatively expensive operation. + +Generally, one should use :c:func:`mmiowb()` prior to releasing a spinlock +that protects regions using :c:func:`writeb()` or similar functions that +aren't surrounded by readb() calls, which will ensure ordering +and flushing. The following pseudocode illustrates what might occur if +write ordering isn't guaranteed via :c:func:`mmiowb()` or one of the +readX() functions:: + + CPU A: spin_lock_irqsave(&dev_lock, flags) + CPU A: ... + CPU A: writel(newval, ring_ptr); + CPU A: spin_unlock_irqrestore(&dev_lock, flags) + ... + CPU B: spin_lock_irqsave(&dev_lock, flags) + CPU B: writel(newval2, ring_ptr); + CPU B: ... + CPU B: spin_unlock_irqrestore(&dev_lock, flags) + +In the case above, newval2 could be written to ring_ptr before newval. +Fixing it is easy though:: + + CPU A: spin_lock_irqsave(&dev_lock, flags) + CPU A: ... + CPU A: writel(newval, ring_ptr); + CPU A: mmiowb(); /* ensure no other writes beat us to the device */ + CPU A: spin_unlock_irqrestore(&dev_lock, flags) + ... + CPU B: spin_lock_irqsave(&dev_lock, flags) + CPU B: writel(newval2, ring_ptr); + CPU B: ... + CPU B: mmiowb(); + CPU B: spin_unlock_irqrestore(&dev_lock, flags) + +See tg3.c for a real world example of how to use :c:func:`mmiowb()` + +PCI ordering rules also guarantee that PIO read responses arrive after any +outstanding DMA writes from that bus, since for some devices the result of +a readb() call may signal to the driver that a DMA transaction is +complete. In many cases, however, the driver may want to indicate that the +next readb() call has no relation to any previous DMA writes +performed by the device. The driver can use readb_relaxed() for +these cases, although only some platforms will honor the relaxed +semantics. Using the relaxed read functions will provide significant +performance benefits on platforms that support it. The qla2xxx driver +provides examples of how to use readX_relaxed(). In many cases, a majority +of the driver's readX() calls can safely be converted to readX_relaxed() +calls, since only a few will indicate or depend on DMA completion. + +Port Space Accesses +=================== + +Port Space Explained +-------------------- + +Another form of IO commonly supported is Port Space. This is a range of +addresses separate to the normal memory address space. Access to these +addresses is generally not as fast as accesses to the memory mapped +addresses, and it also has a potentially smaller address space. + +Unlike memory mapped IO, no preparation is required to access port +space. + +Accessing Port Space +-------------------- + +Accesses to this space are provided through a set of functions which +allow 8-bit, 16-bit and 32-bit accesses; also known as byte, word and +long. These functions are :c:func:`inb()`, :c:func:`inw()`, +:c:func:`inl()`, :c:func:`outb()`, :c:func:`outw()` and +:c:func:`outl()`. + +Some variants are provided for these functions. Some devices require +that accesses to their ports are slowed down. This functionality is +provided by appending a ``_p`` to the end of the function. +There are also equivalents to memcpy. The :c:func:`ins()` and +:c:func:`outs()` functions copy bytes, words or longs to the given +port. + +Public Functions Provided +========================= + +.. kernel-doc:: arch/x86/include/asm/io.h + :internal: + +.. kernel-doc:: lib/pci_iomap.c + :export: diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index a2e5db07756c..365ce64abd7c 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -16,6 +16,7 @@ available subsections can be seen below. basics infrastructure + device-io dma-buf device_link message-based -- cgit v1.2.3 From 028f25332c4f7e8befb22e12eaedd105cd45acb2 Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Fri, 27 Jan 2017 16:50:34 -0700 Subject: docs: Convert the regulator docbook to RST A fairly straightforward conversion to RST; the document is then added to the driver-api manual. Of course, this document has seen no substantive changes since 2008, so chances are it needs work in other areas as well. Cc: Mark Brown Signed-off-by: Jonathan Corbet --- Documentation/DocBook/regulator.tmpl | 304 --------------------------------- Documentation/driver-api/index.rst | 1 + Documentation/driver-api/regulator.rst | 170 ++++++++++++++++++ 3 files changed, 171 insertions(+), 304 deletions(-) delete mode 100644 Documentation/DocBook/regulator.tmpl create mode 100644 Documentation/driver-api/regulator.rst (limited to 'Documentation') diff --git a/Documentation/DocBook/regulator.tmpl b/Documentation/DocBook/regulator.tmpl deleted file mode 100644 index 3b08a085d2c7..000000000000 --- a/Documentation/DocBook/regulator.tmpl +++ /dev/null @@ -1,304 +0,0 @@ - - - - - - Voltage and current regulator API - - - - Liam - Girdwood - -
- lrg@slimlogic.co.uk -
- - - - Mark - Brown - - Wolfson Microelectronics -
- broonie@opensource.wolfsonmicro.com -
- - - - - - 2007-2008 - Wolfson Microelectronics - - - 2008 - Liam Girdwood - - - - - This documentation is free software; you can redistribute - it and/or modify it under the terms of the GNU General Public - License version 2 as published by the Free Software Foundation. - - - - This program is distributed in the hope that it will be - useful, but WITHOUT ANY WARRANTY; without even the implied - warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. - See the GNU General Public License for more details. - - - - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - - - - For more details see the file COPYING in the source - distribution of Linux. - - - - - - - - Introduction - - This framework is designed to provide a standard kernel - interface to control voltage and current regulators. - - - The intention is to allow systems to dynamically control - regulator power output in order to save power and prolong - battery life. This applies to both voltage regulators (where - voltage output is controllable) and current sinks (where current - limit is controllable). - - - Note that additional (and currently more complete) documentation - is available in the Linux kernel source under - Documentation/power/regulator. - - - - Glossary - - The regulator API uses a number of terms which may not be - familiar: - - - - - Regulator - - - Electronic device that supplies power to other devices. Most - regulators can enable and disable their output and some can also - control their output voltage or current. - - - - - - Consumer - - - Electronic device which consumes power provided by a regulator. - These may either be static, requiring only a fixed supply, or - dynamic, requiring active management of the regulator at - runtime. - - - - - - Power Domain - - - The electronic circuit supplied by a given regulator, including - the regulator and all consumer devices. The configuration of - the regulator is shared between all the components in the - circuit. - - - - - - Power Management Integrated Circuit - PMIC - - - An IC which contains numerous regulators and often also other - subsystems. In an embedded system the primary PMIC is often - equivalent to a combination of the PSU and southbridge in a - desktop system. - - - - - - - - - Consumer driver interface - - This offers a similar API to the kernel clock framework. - Consumer drivers use get and put operations to acquire and - release regulators. Functions are - provided to enable - and disable the - regulator and to get and set the runtime parameters of the - regulator. - - - When requesting regulators consumers use symbolic names for their - supplies, such as "Vcc", which are mapped into actual regulator - devices by the machine interface. - - - A stub version of this API is provided when the regulator - framework is not in use in order to minimise the need to use - ifdefs. - - - - Enabling and disabling - - The regulator API provides reference counted enabling and - disabling of regulators. Consumer devices use the regulator_enable - and regulator_disable - functions to enable and disable regulators. Calls - to the two functions must be balanced. - - - Note that since multiple consumers may be using a regulator and - machine constraints may not allow the regulator to be disabled - there is no guarantee that calling - regulator_disable will actually cause the - supply provided by the regulator to be disabled. Consumer - drivers should assume that the regulator may be enabled at all - times. - - - - - Configuration - - Some consumer devices may need to be able to dynamically - configure their supplies. For example, MMC drivers may need to - select the correct operating voltage for their cards. This may - be done while the regulator is enabled or disabled. - - - The regulator_set_voltage - and regulator_set_current_limit - functions provide the primary interface for this. - Both take ranges of voltages and currents, supporting drivers - that do not require a specific value (eg, CPU frequency scaling - normally permits the CPU to use a wider range of supply - voltages at lower frequencies but does not require that the - supply voltage be lowered). Where an exact value is required - both minimum and maximum values should be identical. - - - - - Callbacks - - Callbacks may also be registered - for events such as regulation failures. - - - - - - Regulator driver interface - - Drivers for regulator chips register the regulators - with the regulator core, providing operations structures to the - core. A notifier interface - allows error conditions to be reported to the core. - - - Registration should be triggered by explicit setup done by the - platform, supplying a struct - regulator_init_data for the regulator containing - constraint and - supply information. - - - - - Machine interface - - This interface provides a way to define how regulators are - connected to consumers on a given system and what the valid - operating parameters are for the system. - - - - Supplies - - Regulator supplies are specified using struct - regulator_consumer_supply. This is done at - driver registration - time as part of the machine constraints. - - - - - Constraints - - As well as defining the connections the machine interface - also provides constraints defining the operations that - clients are allowed to perform and the parameters that may be - set. This is required since generally regulator devices will - offer more flexibility than it is safe to use on a given - system, for example supporting higher supply voltages than the - consumers are rated for. - - - This is done at driver - registration time by providing a struct - regulation_constraints. - - - The constraints may also specify an initial configuration for the - regulator in the constraints, which is particularly useful for - use with static consumers. - - - - - - API reference - - Due to limitations of the kernel documentation framework and the - existing layout of the source code the entire regulator API is - documented here. - -!Iinclude/linux/regulator/consumer.h -!Iinclude/linux/regulator/machine.h -!Iinclude/linux/regulator/driver.h -!Edrivers/regulator/core.c - - diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index 365ce64abd7c..9cdf81b59ec5 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -22,6 +22,7 @@ available subsections can be seen below. message-based sound frame-buffer + regulator iio/index input usb diff --git a/Documentation/driver-api/regulator.rst b/Documentation/driver-api/regulator.rst new file mode 100644 index 000000000000..520da0a5251d --- /dev/null +++ b/Documentation/driver-api/regulator.rst @@ -0,0 +1,170 @@ +.. Copyright 2007-2008 Wolfson Microelectronics + +.. This documentation is free software; you can redistribute +.. it and/or modify it under the terms of the GNU General Public +.. License version 2 as published by the Free Software Foundation. + +================================= +Voltage and current regulator API +================================= + +:Author: Liam Girdwood +:Author: Mark Brown + +Introduction +============ + +This framework is designed to provide a standard kernel interface to +control voltage and current regulators. + +The intention is to allow systems to dynamically control regulator power +output in order to save power and prolong battery life. This applies to +both voltage regulators (where voltage output is controllable) and +current sinks (where current limit is controllable). + +Note that additional (and currently more complete) documentation is +available in the Linux kernel source under +``Documentation/power/regulator``. + +Glossary +-------- + +The regulator API uses a number of terms which may not be familiar: + +Regulator + + Electronic device that supplies power to other devices. Most regulators + can enable and disable their output and some can also control their + output voltage or current. + +Consumer + + Electronic device which consumes power provided by a regulator. These + may either be static, requiring only a fixed supply, or dynamic, + requiring active management of the regulator at runtime. + +Power Domain + + The electronic circuit supplied by a given regulator, including the + regulator and all consumer devices. The configuration of the regulator + is shared between all the components in the circuit. + +Power Management Integrated Circuit (PMIC) + + An IC which contains numerous regulators and often also other + subsystems. In an embedded system the primary PMIC is often equivalent + to a combination of the PSU and southbridge in a desktop system. + +Consumer driver interface +========================= + +This offers a similar API to the kernel clock framework. Consumer +drivers use `get <#API-regulator-get>`__ and +`put <#API-regulator-put>`__ operations to acquire and release +regulators. Functions are provided to `enable <#API-regulator-enable>`__ +and `disable <#API-regulator-disable>`__ the regulator and to get and +set the runtime parameters of the regulator. + +When requesting regulators consumers use symbolic names for their +supplies, such as "Vcc", which are mapped into actual regulator devices +by the machine interface. + +A stub version of this API is provided when the regulator framework is +not in use in order to minimise the need to use ifdefs. + +Enabling and disabling +---------------------- + +The regulator API provides reference counted enabling and disabling of +regulators. Consumer devices use the :c:func:`regulator_enable()` and +:c:func:`regulator_disable()` functions to enable and disable +regulators. Calls to the two functions must be balanced. + +Note that since multiple consumers may be using a regulator and machine +constraints may not allow the regulator to be disabled there is no +guarantee that calling :c:func:`regulator_disable()` will actually +cause the supply provided by the regulator to be disabled. Consumer +drivers should assume that the regulator may be enabled at all times. + +Configuration +------------- + +Some consumer devices may need to be able to dynamically configure their +supplies. For example, MMC drivers may need to select the correct +operating voltage for their cards. This may be done while the regulator +is enabled or disabled. + +The :c:func:`regulator_set_voltage()` and +:c:func:`regulator_set_current_limit()` functions provide the primary +interface for this. Both take ranges of voltages and currents, supporting +drivers that do not require a specific value (eg, CPU frequency scaling +normally permits the CPU to use a wider range of supply voltages at lower +frequencies but does not require that the supply voltage be lowered). Where +an exact value is required both minimum and maximum values should be +identical. + +Callbacks +--------- + +Callbacks may also be registered for events such as regulation failures. + +Regulator driver interface +========================== + +Drivers for regulator chips register the regulators with the regulator +core, providing operations structures to the core. A notifier interface +allows error conditions to be reported to the core. + +Registration should be triggered by explicit setup done by the platform, +supplying a struct :c:type:`regulator_init_data` for the regulator +containing constraint and supply information. + +Machine interface +================= + +This interface provides a way to define how regulators are connected to +consumers on a given system and what the valid operating parameters are +for the system. + +Supplies +-------- + +Regulator supplies are specified using struct +:c:type:`regulator_consumer_supply`. This is done at driver registration +time as part of the machine constraints. + +Constraints +----------- + +As well as defining the connections the machine interface also provides +constraints defining the operations that clients are allowed to perform +and the parameters that may be set. This is required since generally +regulator devices will offer more flexibility than it is safe to use on +a given system, for example supporting higher supply voltages than the +consumers are rated for. + +This is done at driver registration time` by providing a +struct :c:type:`regulation_constraints`. + +The constraints may also specify an initial configuration for the +regulator in the constraints, which is particularly useful for use with +static consumers. + +API reference +============= + +Due to limitations of the kernel documentation framework and the +existing layout of the source code the entire regulator API is +documented here. + +.. kernel-doc:: include/linux/regulator/consumer.h + :internal: + +.. kernel-doc:: include/linux/regulator/machine.h + :internal: + +.. kernel-doc:: include/linux/regulator/driver.h + :internal: + +.. kernel-doc:: drivers/regulator/core.c + :export: -- cgit v1.2.3 From 2a0f4038a4919712a62031dc63aa871a84b4ad05 Mon Sep 17 00:00:00 2001 From: Jani Nikula Date: Tue, 31 Jan 2017 20:18:05 +0200 Subject: Documentation/sphinx: prevent generation of .pyc files in the source tree Use PYTHONDONTWRITEBYTECODE=1 to prevent python from creating .pyc files in the source tree. Python 3.2 has a __pycache__ scheme [1], but before that the only alternative seems to be to copy the source files to the build tree to ensure the .pyc files are created there too. Just prevent .pyc file generation for simplicity. Considering the small amount of python code to compile (assuming sphinx itself has .pyc around), the impact on build is neglible. [1] http://stackoverflow.com/questions/3522079/changing-the-directory-where-pyc-files-are-created References: http://lkml.kernel.org/r/CAMuHMdVxqpH7-9XJ+YE_pgoA+-fe0969cSkOehYh3uubYcrhZA@mail.gmail.com Reported-by: Geert Uytterhoeven References: http://lkml.kernel.org/r/1485816692.2900.17.camel@decadent.org.uk Reported-by: Ben Hutchings Cc: Jonathan Corbet Signed-off-by: Jani Nikula Signed-off-by: Jonathan Corbet --- Documentation/Makefile.sphinx | 1 + 1 file changed, 1 insertion(+) (limited to 'Documentation') diff --git a/Documentation/Makefile.sphinx b/Documentation/Makefile.sphinx index 707c65337ebf..91f541a52884 100644 --- a/Documentation/Makefile.sphinx +++ b/Documentation/Makefile.sphinx @@ -55,6 +55,7 @@ loop_cmd = $(echo-cmd) $(cmd_$(1)) quiet_cmd_sphinx = SPHINX $@ --> file://$(abspath $(BUILDDIR)/$3/$4) cmd_sphinx = $(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media $2;\ + PYTHONDONTWRITEBYTECODE=1 \ BUILDDIR=$(abspath $(BUILDDIR)) SPHINX_CONF=$(abspath $(srctree)/$(src)/$5/$(SPHINX_CONF)) \ $(SPHINXBUILD) \ -b $2 \ -- cgit v1.2.3 From 7cabd5ac69a4135fd8dbc1f1bb9c9531a5f1e5c7 Mon Sep 17 00:00:00 2001 From: Markus Heiser Date: Tue, 31 Jan 2017 10:57:41 +0100 Subject: doc-rst: fixed cleandoc target when used with O=dir The cleandocs target won't work if I use a different output folder:: $ make O=/tmp/kernel SPHINXDIRS="process" cleandocs make[1]: Entering directory '/tmp/kernel' make[3]: *** No rule to make target 'clean'. Stop. ... Documentation/Makefile.sphinx:100: recipe for target 'cleandocs' failed Signed-off-by: Markus Heiser Signed-off-by: Jonathan Corbet --- Documentation/Makefile.sphinx | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/Makefile.sphinx b/Documentation/Makefile.sphinx index 91f541a52884..b88f666f72bb 100644 --- a/Documentation/Makefile.sphinx +++ b/Documentation/Makefile.sphinx @@ -99,7 +99,7 @@ installmandocs: cleandocs: $(Q)rm -rf $(BUILDDIR) - $(Q)$(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) -C Documentation/media clean + $(Q)$(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media clean endif # HAVE_SPHINX -- cgit v1.2.3 From c8929258a59b784a61dc0bbe3cfca6ebed5f47c4 Mon Sep 17 00:00:00 2001 From: Jani Nikula Date: Mon, 30 Jan 2017 18:58:15 +0200 Subject: Documentation/sphinx: make targets independent of Sphinx work for HAVE_SPHINX=0 Make targets that don't depend on Sphinx work without warnings about missing Sphinx. 'make cleandocs' will work without Sphinx just fine, and the targets that are no-ops for Sphinx should just be skipped. Move them outside of the HAVE_SPHINX checks to take precedence over the .DEFAULT target for HAVE_SPHINX=0. Reported-by: Jim Davis Reference: http://lkml.kernel.org/r/CA+r1ZhjRVqkjPXGOGB_BOAX2Hkfb+qQCtTzFfBMFeH1Mfeej7w@mail.gmail.com Signed-off-by: Jani Nikula Signed-off-by: Jonathan Corbet --- Documentation/Makefile.sphinx | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/Makefile.sphinx b/Documentation/Makefile.sphinx index b88f666f72bb..fd32fc727777 100644 --- a/Documentation/Makefile.sphinx +++ b/Documentation/Makefile.sphinx @@ -91,6 +91,11 @@ epubdocs: xmldocs: @$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,xml,$(var),xml,$(var))) +endif # HAVE_SPHINX + +# The following targets are independent of HAVE_SPHINX, and the rules should +# work or silently pass without Sphinx. + # no-ops for the Sphinx toolchain sgmldocs: psdocs: @@ -101,8 +106,6 @@ cleandocs: $(Q)rm -rf $(BUILDDIR) $(Q)$(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media clean -endif # HAVE_SPHINX - dochelp: @echo ' Linux kernel internal documentation in different formats (Sphinx):' @echo ' htmldocs - HTML' -- cgit v1.2.3 From 85bd9020d86bf51f9c300225d0c4d7d1b5aa9e48 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Tue, 31 Jan 2017 00:18:34 +0000 Subject: doc-rst: Break shell command sequences on failure As $(SHELL) doesn't include the -e option, any loop or other sequence needs to include explicit checks for failing commands. Fixes: 609afe6b49ef ("Documentation/sphinx: build the media intermediate ...") Fixes: 606b9ac81a63 ("doc-rst: generic way to build only sphinx sub-folders") Fixes: cd21379b1698 ("doc-rst: generic way to build PDF of sub-folders") Tested-by: Markus Heiser Signed-off-by: Ben Hutchings Signed-off-by: Jonathan Corbet --- Documentation/Makefile.sphinx | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'Documentation') diff --git a/Documentation/Makefile.sphinx b/Documentation/Makefile.sphinx index 707c65337ebf..02d84e6dc7fc 100644 --- a/Documentation/Makefile.sphinx +++ b/Documentation/Makefile.sphinx @@ -43,7 +43,7 @@ ALLSPHINXOPTS = $(KERNELDOC_CONF) $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) I18NSPHINXOPTS = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) . # commands; the 'cmd' from scripts/Kbuild.include is not *loopable* -loop_cmd = $(echo-cmd) $(cmd_$(1)) +loop_cmd = $(echo-cmd) $(cmd_$(1)) || exit; # $2 sphinx builder e.g. "html" # $3 name of the build subfolder / e.g. "media", used as: @@ -54,7 +54,7 @@ loop_cmd = $(echo-cmd) $(cmd_$(1)) # e.g. "media" for the linux-tv book-set at ./Documentation/media quiet_cmd_sphinx = SPHINX $@ --> file://$(abspath $(BUILDDIR)/$3/$4) - cmd_sphinx = $(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media $2;\ + cmd_sphinx = $(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media $2 && \ BUILDDIR=$(abspath $(BUILDDIR)) SPHINX_CONF=$(abspath $(srctree)/$(src)/$5/$(SPHINX_CONF)) \ $(SPHINXBUILD) \ -b $2 \ @@ -63,7 +63,7 @@ quiet_cmd_sphinx = SPHINX $@ --> file://$(abspath $(BUILDDIR)/$3/$4) -D version=$(KERNELVERSION) -D release=$(KERNELRELEASE) \ $(ALLSPHINXOPTS) \ $(abspath $(srctree)/$(src)/$5) \ - $(abspath $(BUILDDIR)/$3/$4); + $(abspath $(BUILDDIR)/$3/$4) htmldocs: @$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,html,$(var),,$(var))) @@ -80,7 +80,7 @@ pdfdocs: else # HAVE_PDFLATEX pdfdocs: latexdocs - $(foreach var,$(SPHINXDIRS), $(MAKE) PDFLATEX=$(PDFLATEX) LATEXOPTS="$(LATEXOPTS)" -C $(BUILDDIR)/$(var)/latex;) + $(foreach var,$(SPHINXDIRS), $(MAKE) PDFLATEX=$(PDFLATEX) LATEXOPTS="$(LATEXOPTS)" -C $(BUILDDIR)/$(var)/latex || exit;) endif # HAVE_PDFLATEX -- cgit v1.2.3 From 04b709117271d9f2f09cfeca09c34f63863beafe Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Tue, 31 Jan 2017 00:18:44 +0000 Subject: doc-rst: Delete output of failed dot-SVG conversion As we use redirection to create the SVG file, even a failed conversion will create the file and 'make' will consider it up-to-date if the build is retried. We should delete it in case of failure. Fixes: ec868e4ee2bc ("docs-rst: media: build SVG from graphviz files") Signed-off-by: Ben Hutchings Signed-off-by: Jonathan Corbet --- Documentation/media/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/media/Makefile b/Documentation/media/Makefile index 32663602ff25..730d73db7c7a 100644 --- a/Documentation/media/Makefile +++ b/Documentation/media/Makefile @@ -36,7 +36,7 @@ quiet_cmd_genpdf = GENPDF $2 cmd_genpdf = convert $2 $3 quiet_cmd_gendot = DOT $2 - cmd_gendot = dot -Tsvg $2 > $3 + cmd_gendot = dot -Tsvg $2 > $3 || { rm -f $3; exit 1; } %.pdf: %.svg @$(call cmd,genpdf,$<,$@) -- cgit v1.2.3 From 4b0b0d9d05aba12b42b2e5006627fa6821bcec62 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Tue, 31 Jan 2017 00:18:56 +0000 Subject: doc-rst: Fix recursive make invocation from macros In any case where we recurse but don't mention $(MAKE) literally in the recipe, we need to add a '+' at the start of the command to ensure that parallel makes and various other options work properly. Fixes: 609afe6b49ef ("Documentation/sphinx: build the media intermediate ...") Tested-by: Markus Heiser Signed-off-by: Ben Hutchings Signed-off-by: Jonathan Corbet --- Documentation/Makefile.sphinx | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'Documentation') diff --git a/Documentation/Makefile.sphinx b/Documentation/Makefile.sphinx index 02d84e6dc7fc..e14d82a98062 100644 --- a/Documentation/Makefile.sphinx +++ b/Documentation/Makefile.sphinx @@ -66,10 +66,10 @@ quiet_cmd_sphinx = SPHINX $@ --> file://$(abspath $(BUILDDIR)/$3/$4) $(abspath $(BUILDDIR)/$3/$4) htmldocs: - @$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,html,$(var),,$(var))) + @+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,html,$(var),,$(var))) latexdocs: - @$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,latex,$(var),latex,$(var))) + @+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,latex,$(var),latex,$(var))) ifeq ($(HAVE_PDFLATEX),0) @@ -85,10 +85,10 @@ pdfdocs: latexdocs endif # HAVE_PDFLATEX epubdocs: - @$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,epub,$(var),epub,$(var))) + @+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,epub,$(var),epub,$(var))) xmldocs: - @$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,xml,$(var),xml,$(var))) + @+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,xml,$(var),xml,$(var))) # no-ops for the Sphinx toolchain sgmldocs: -- cgit v1.2.3 From 2728b2d2e5be4b828a523a06089cd605419fc65c Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Thu, 2 Feb 2017 01:32:13 +0100 Subject: PM / core / docs: Convert sleep states API document to reST Move the document describing the system sleep state transitions API for devices to Documentation/driver-api/pm/, convert it to reST and update it to use current terminology. Also remove the remaining reference to the old version of it from pm.h. The new document still contains references to some documents in the .txt format that will be converted later. Signed-off-by: Rafael J. Wysocki Signed-off-by: Jonathan Corbet --- Documentation/driver-api/index.rst | 1 + Documentation/driver-api/pm/conf.py | 10 + Documentation/driver-api/pm/devices.rst | 732 ++++++++++++++++++++++++++++++++ Documentation/driver-api/pm/index.rst | 15 + Documentation/driver-api/pm/types.rst | 5 + Documentation/power/devices.txt | 716 ------------------------------- include/linux/pm.h | 3 - 7 files changed, 763 insertions(+), 719 deletions(-) create mode 100644 Documentation/driver-api/pm/conf.py create mode 100644 Documentation/driver-api/pm/devices.rst create mode 100644 Documentation/driver-api/pm/index.rst create mode 100644 Documentation/driver-api/pm/types.rst delete mode 100644 Documentation/power/devices.txt (limited to 'Documentation') diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index 9cdf81b59ec5..ea580c0aa232 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -16,6 +16,7 @@ available subsections can be seen below. basics infrastructure + pm/index device-io dma-buf device_link diff --git a/Documentation/driver-api/pm/conf.py b/Documentation/driver-api/pm/conf.py new file mode 100644 index 000000000000..a89fac11272f --- /dev/null +++ b/Documentation/driver-api/pm/conf.py @@ -0,0 +1,10 @@ +# -*- coding: utf-8; mode: python -*- + +project = "Device Power Management" + +tags.add("subproject") + +latex_documents = [ + ('index', 'pm.tex', project, + 'The kernel development community', 'manual'), +] diff --git a/Documentation/driver-api/pm/devices.rst b/Documentation/driver-api/pm/devices.rst new file mode 100644 index 000000000000..f165cf6f733e --- /dev/null +++ b/Documentation/driver-api/pm/devices.rst @@ -0,0 +1,732 @@ +.. |struct| replace:: :c:type:`struct` + +============================== +Device Power Management Basics +============================== + +:: + + Copyright (c) 2010-2011 Rafael J. Wysocki , Novell Inc. + Copyright (c) 2010 Alan Stern + Copyright (c) 2016 Intel Corp., Rafael J. Wysocki + +Most of the code in Linux is device drivers, so most of the Linux power +management (PM) code is also driver-specific. Most drivers will do very +little; others, especially for platforms with small batteries (like cell +phones), will do a lot. + +This writeup gives an overview of how drivers interact with system-wide +power management goals, emphasizing the models and interfaces that are +shared by everything that hooks up to the driver model core. Read it as +background for the domain-specific work you'd do with any specific driver. + + +Two Models for Device Power Management +====================================== + +Drivers will use one or both of these models to put devices into low-power +states: + + System Sleep model: + + Drivers can enter low-power states as part of entering system-wide + low-power states like "suspend" (also known as "suspend-to-RAM"), or + (mostly for systems with disks) "hibernation" (also known as + "suspend-to-disk"). + + This is something that device, bus, and class drivers collaborate on + by implementing various role-specific suspend and resume methods to + cleanly power down hardware and software subsystems, then reactivate + them without loss of data. + + Some drivers can manage hardware wakeup events, which make the system + leave the low-power state. This feature may be enabled or disabled + using the relevant :file:`/sys/devices/.../power/wakeup` file (for + Ethernet drivers the ioctl interface used by ethtool may also be used + for this purpose); enabling it may cost some power usage, but let the + whole system enter low-power states more often. + + Runtime Power Management model: + + Devices may also be put into low-power states while the system is + running, independently of other power management activity in principle. + However, devices are not generally independent of each other (for + example, a parent device cannot be suspended unless all of its child + devices have been suspended). Moreover, depending on the bus type the + device is on, it may be necessary to carry out some bus-specific + operations on the device for this purpose. Devices put into low power + states at run time may require special handling during system-wide power + transitions (suspend or hibernation). + + For these reasons not only the device driver itself, but also the + appropriate subsystem (bus type, device type or device class) driver and + the PM core are involved in runtime power management. As in the system + sleep power management case, they need to collaborate by implementing + various role-specific suspend and resume methods, so that the hardware + is cleanly powered down and reactivated without data or service loss. + +There's not a lot to be said about those low-power states except that they are +very system-specific, and often device-specific. Also, that if enough devices +have been put into low-power states (at runtime), the effect may be very similar +to entering some system-wide low-power state (system sleep) ... and that +synergies exist, so that several drivers using runtime PM might put the system +into a state where even deeper power saving options are available. + +Most suspended devices will have quiesced all I/O: no more DMA or IRQs (except +for wakeup events), no more data read or written, and requests from upstream +drivers are no longer accepted. A given bus or platform may have different +requirements though. + +Examples of hardware wakeup events include an alarm from a real time clock, +network wake-on-LAN packets, keyboard or mouse activity, and media insertion +or removal (for PCMCIA, MMC/SD, USB, and so on). + +Interfaces for Entering System Sleep States +=========================================== + +There are programming interfaces provided for subsystems (bus type, device type, +device class) and device drivers to allow them to participate in the power +management of devices they are concerned with. These interfaces cover both +system sleep and runtime power management. + + +Device Power Management Operations +---------------------------------- + +Device power management operations, at the subsystem level as well as at the +device driver level, are implemented by defining and populating objects of type +|struct| :c:type:`dev_pm_ops` defined in :file:`include/linux/pm.h`. +The roles of the methods included in it will be explained in what follows. For +now, it should be sufficient to remember that the last three methods are +specific to runtime power management while the remaining ones are used during +system-wide power transitions. + +There also is a deprecated "old" or "legacy" interface for power management +operations available at least for some subsystems. This approach does not use +|struct| :c:type:`dev_pm_ops` objects and it is suitable only for implementing +system sleep power management methods in a limited way. Therefore it is not +described in this document, so please refer directly to the source code for more +information about it. + + +Subsystem-Level Methods +----------------------- + +The core methods to suspend and resume devices reside in +|struct| :c:type:`dev_pm_ops` pointed to by the :c:member:`ops` +member of |struct| :c:type:`dev_pm_domain`, or by the :c:member:`pm` +member of |struct| :c:type:`bus_type`, |struct| :c:type:`device_type` and +|struct| :c:type:`class`. They are mostly of interest to the people writing +infrastructure for platforms and buses, like PCI or USB, or device type and +device class drivers. They also are relevant to the writers of device drivers +whose subsystems (PM domains, device types, device classes and bus types) don't +provide all power management methods. + +Bus drivers implement these methods as appropriate for the hardware and the +drivers using it; PCI works differently from USB, and so on. Not many people +write subsystem-level drivers; most driver code is a "device driver" that builds +on top of bus-specific framework code. + +For more information on these driver calls, see the description later; +they are called in phases for every device, respecting the parent-child +sequencing in the driver model tree. + + +:file:`/sys/devices/.../power/wakeup` files +------------------------------------------- + +All device objects in the driver model contain fields that control the handling +of system wakeup events (hardware signals that can force the system out of a +sleep state). These fields are initialized by bus or device driver code using +:c:func:`device_set_wakeup_capable()` and :c:func:`device_set_wakeup_enable()`, +defined in :file:`include/linux/pm_wakeup.h`. + +The :c:member:`power.can_wakeup` flag just records whether the device (and its +driver) can physically support wakeup events. The +:c:func:`device_set_wakeup_capable()` routine affects this flag. The +:c:member:`power.wakeup` field is a pointer to an object of type +|struct| :c:type:`wakeup_source` used for controlling whether or not +the device should use its system wakeup mechanism and for notifying the +PM core of system wakeup events signaled by the device. This object is only +present for wakeup-capable devices (i.e. devices whose +:c:member:`can_wakeup` flags are set) and is created (or removed) by +:c:func:`device_set_wakeup_capable()`. + +Whether or not a device is capable of issuing wakeup events is a hardware +matter, and the kernel is responsible for keeping track of it. By contrast, +whether or not a wakeup-capable device should issue wakeup events is a policy +decision, and it is managed by user space through a sysfs attribute: the +:file:`power/wakeup` file. User space can write the "enabled" or "disabled" +strings to it to indicate whether or not, respectively, the device is supposed +to signal system wakeup. This file is only present if the +:c:member:`power.wakeup` object exists for the given device and is created (or +removed) along with that object, by :c:func:`device_set_wakeup_capable()`. +Reads from the file will return the corresponding string. + +The initial value in the :file:`power/wakeup` file is "disabled" for the +majority of devices; the major exceptions are power buttons, keyboards, and +Ethernet adapters whose WoL (wake-on-LAN) feature has been set up with ethtool. +It should also default to "enabled" for devices that don't generate wakeup +requests on their own but merely forward wakeup requests from one bus to another +(like PCI Express ports). + +The :c:func:`device_may_wakeup()` routine returns true only if the +:c:member:`power.wakeup` object exists and the corresponding :file:`power/wakeup` +file contains the "enabled" string. This information is used by subsystems, +like the PCI bus type code, to see whether or not to enable the devices' wakeup +mechanisms. If device wakeup mechanisms are enabled or disabled directly by +drivers, they also should use :c:func:`device_may_wakeup()` to decide what to do +during a system sleep transition. Device drivers, however, are not expected to +call :c:func:`device_set_wakeup_enable()` directly in any case. + +It ought to be noted that system wakeup is conceptually different from "remote +wakeup" used by runtime power management, although it may be supported by the +same physical mechanism. Remote wakeup is a feature allowing devices in +low-power states to trigger specific interrupts to signal conditions in which +they should be put into the full-power state. Those interrupts may or may not +be used to signal system wakeup events, depending on the hardware design. On +some systems it is impossible to trigger them from system sleep states. In any +case, remote wakeup should always be enabled for runtime power management for +all devices and drivers that support it. + + +:file:`/sys/devices/.../power/control` files +-------------------------------------------- + +Each device in the driver model has a flag to control whether it is subject to +runtime power management. This flag, :c:member:`runtime_auto`, is initialized +by the bus type (or generally subsystem) code using :c:func:`pm_runtime_allow()` +or :c:func:`pm_runtime_forbid()`; the default is to allow runtime power +management. + +The setting can be adjusted by user space by writing either "on" or "auto" to +the device's :file:`power/control` sysfs file. Writing "auto" calls +:c:func:`pm_runtime_allow()`, setting the flag and allowing the device to be +runtime power-managed by its driver. Writing "on" calls +:c:func:`pm_runtime_forbid()`, clearing the flag, returning the device to full +power if it was in a low-power state, and preventing the +device from being runtime power-managed. User space can check the current value +of the :c:member:`runtime_auto` flag by reading that file. + +The device's :c:member:`runtime_auto` flag has no effect on the handling of +system-wide power transitions. In particular, the device can (and in the +majority of cases should and will) be put into a low-power state during a +system-wide transition to a sleep state even though its :c:member:`runtime_auto` +flag is clear. + +For more information about the runtime power management framework, refer to +:file:`Documentation/power/runtime_pm.txt`. + + +Calling Drivers to Enter and Leave System Sleep States +====================================================== + +When the system goes into a sleep state, each device's driver is asked to +suspend the device by putting it into a state compatible with the target +system state. That's usually some version of "off", but the details are +system-specific. Also, wakeup-enabled devices will usually stay partly +functional in order to wake the system. + +When the system leaves that low-power state, the device's driver is asked to +resume it by returning it to full power. The suspend and resume operations +always go together, and both are multi-phase operations. + +For simple drivers, suspend might quiesce the device using class code +and then turn its hardware as "off" as possible during suspend_noirq. The +matching resume calls would then completely reinitialize the hardware +before reactivating its class I/O queues. + +More power-aware drivers might prepare the devices for triggering system wakeup +events. + + +Call Sequence Guarantees +------------------------ + +To ensure that bridges and similar links needing to talk to a device are +available when the device is suspended or resumed, the device hierarchy is +walked in a bottom-up order to suspend devices. A top-down order is +used to resume those devices. + +The ordering of the device hierarchy is defined by the order in which devices +get registered: a child can never be registered, probed or resumed before +its parent; and can't be removed or suspended after that parent. + +The policy is that the device hierarchy should match hardware bus topology. +[Or at least the control bus, for devices which use multiple busses.] +In particular, this means that a device registration may fail if the parent of +the device is suspending (i.e. has been chosen by the PM core as the next +device to suspend) or has already suspended, as well as after all of the other +devices have been suspended. Device drivers must be prepared to cope with such +situations. + + +System Power Management Phases +------------------------------ + +Suspending or resuming the system is done in several phases. Different phases +are used for suspend-to-idle, shallow (standby), and deep ("suspend-to-RAM") +sleep states and the hibernation state ("suspend-to-disk"). Each phase involves +executing callbacks for every device before the next phase begins. Not all +buses or classes support all these callbacks and not all drivers use all the +callbacks. The various phases always run after tasks have been frozen and +before they are unfrozen. Furthermore, the ``*_noirq phases`` run at a time +when IRQ handlers have been disabled (except for those marked with the +IRQF_NO_SUSPEND flag). + +All phases use PM domain, bus, type, class or driver callbacks (that is, methods +defined in ``dev->pm_domain->ops``, ``dev->bus->pm``, ``dev->type->pm``, +``dev->class->pm`` or ``dev->driver->pm``). These callbacks are regarded by the +PM core as mutually exclusive. Moreover, PM domain callbacks always take +precedence over all of the other callbacks and, for example, type callbacks take +precedence over bus, class and driver callbacks. To be precise, the following +rules are used to determine which callback to execute in the given phase: + + 1. If ``dev->pm_domain`` is present, the PM core will choose the callback + provided by ``dev->pm_domain->ops`` for execution. + + 2. Otherwise, if both ``dev->type`` and ``dev->type->pm`` are present, the + callback provided by ``dev->type->pm`` will be chosen for execution. + + 3. Otherwise, if both ``dev->class`` and ``dev->class->pm`` are present, + the callback provided by ``dev->class->pm`` will be chosen for + execution. + + 4. Otherwise, if both ``dev->bus`` and ``dev->bus->pm`` are present, the + callback provided by ``dev->bus->pm`` will be chosen for execution. + +This allows PM domains and device types to override callbacks provided by bus +types or device classes if necessary. + +The PM domain, type, class and bus callbacks may in turn invoke device- or +driver-specific methods stored in ``dev->driver->pm``, but they don't have to do +that. + +If the subsystem callback chosen for execution is not present, the PM core will +execute the corresponding method from the ``dev->driver->pm`` set instead if +there is one. + + +Entering System Suspend +----------------------- + +When the system goes into the freeze, standby or memory sleep state, +the phases are: ``prepare``, ``suspend``, ``suspend_late``, ``suspend_noirq``. + + 1. The ``prepare`` phase is meant to prevent races by preventing new + devices from being registered; the PM core would never know that all the + children of a device had been suspended if new children could be + registered at will. [By contrast, from the PM core's perspective, + devices may be unregistered at any time.] Unlike the other + suspend-related phases, during the ``prepare`` phase the device + hierarchy is traversed top-down. + + After the ``->prepare`` callback method returns, no new children may be + registered below the device. The method may also prepare the device or + driver in some way for the upcoming system power transition, but it + should not put the device into a low-power state. + + For devices supporting runtime power management, the return value of the + prepare callback can be used to indicate to the PM core that it may + safely leave the device in runtime suspend (if runtime-suspended + already), provided that all of the device's descendants are also left in + runtime suspend. Namely, if the prepare callback returns a positive + number and that happens for all of the descendants of the device too, + and all of them (including the device itself) are runtime-suspended, the + PM core will skip the ``suspend``, ``suspend_late`` and + ``suspend_noirq`` phases as well as all of the corresponding phases of + the subsequent device resume for all of these devices. In that case, + the ``->complete`` callback will be invoked directly after the + ``->prepare`` callback and is entirely responsible for putting the + device into a consistent state as appropriate. + + Note that this direct-complete procedure applies even if the device is + disabled for runtime PM; only the runtime-PM status matters. It follows + that if a device has system-sleep callbacks but does not support runtime + PM, then its prepare callback must never return a positive value. This + is because all such devices are initially set to runtime-suspended with + runtime PM disabled. + + 2. The ``->suspend`` methods should quiesce the device to stop it from + performing I/O. They also may save the device registers and put it into + the appropriate low-power state, depending on the bus type the device is + on, and they may enable wakeup events. + + 3. For a number of devices it is convenient to split suspend into the + "quiesce device" and "save device state" phases, in which cases + ``suspend_late`` is meant to do the latter. It is always executed after + runtime power management has been disabled for the device in question. + + 4. The ``suspend_noirq`` phase occurs after IRQ handlers have been disabled, + which means that the driver's interrupt handler will not be called while + the callback method is running. The ``->suspend_noirq`` methods should + save the values of the device's registers that weren't saved previously + and finally put the device into the appropriate low-power state. + + The majority of subsystems and device drivers need not implement this + callback. However, bus types allowing devices to share interrupt + vectors, like PCI, generally need it; otherwise a driver might encounter + an error during the suspend phase by fielding a shared interrupt + generated by some other device after its own device had been set to low + power. + +At the end of these phases, drivers should have stopped all I/O transactions +(DMA, IRQs), saved enough state that they can re-initialize or restore previous +state (as needed by the hardware), and placed the device into a low-power state. +On many platforms they will gate off one or more clock sources; sometimes they +will also switch off power supplies or reduce voltages. [Drivers supporting +runtime PM may already have performed some or all of these steps.] + +If :c:func:`device_may_wakeup(dev)` returns ``true``, the device should be +prepared for generating hardware wakeup signals to trigger a system wakeup event +when the system is in the sleep state. For example, :c:func:`enable_irq_wake()` +might identify GPIO signals hooked up to a switch or other external hardware, +and :c:func:`pci_enable_wake()` does something similar for the PCI PME signal. + +If any of these callbacks returns an error, the system won't enter the desired +low-power state. Instead, the PM core will unwind its actions by resuming all +the devices that were suspended. + + +Leaving System Suspend +---------------------- + +When resuming from freeze, standby or memory sleep, the phases are: +``resume_noirq``, ``resume_early``, ``resume``, ``complete``. + + 1. The ``->resume_noirq`` callback methods should perform any actions + needed before the driver's interrupt handlers are invoked. This + generally means undoing the actions of the ``suspend_noirq`` phase. If + the bus type permits devices to share interrupt vectors, like PCI, the + method should bring the device and its driver into a state in which the + driver can recognize if the device is the source of incoming interrupts, + if any, and handle them correctly. + + For example, the PCI bus type's ``->pm.resume_noirq()`` puts the device + into the full-power state (D0 in the PCI terminology) and restores the + standard configuration registers of the device. Then it calls the + device driver's ``->pm.resume_noirq()`` method to perform device-specific + actions. + + 2. The ``->resume_early`` methods should prepare devices for the execution + of the resume methods. This generally involves undoing the actions of + the preceding ``suspend_late`` phase. + + 3. The ``->resume`` methods should bring the device back to its operating + state, so that it can perform normal I/O. This generally involves + undoing the actions of the ``suspend`` phase. + + 4. The ``complete`` phase should undo the actions of the ``prepare`` phase. + For this reason, unlike the other resume-related phases, during the + ``complete`` phase the device hierarchy is traversed bottom-up. + + Note, however, that new children may be registered below the device as + soon as the ``->resume`` callbacks occur; it's not necessary to wait + until the ``complete`` phase with that. + + Moreover, if the preceding ``->prepare`` callback returned a positive + number, the device may have been left in runtime suspend throughout the + whole system suspend and resume (the ``suspend``, ``suspend_late``, + ``suspend_noirq`` phases of system suspend and the ``resume_noirq``, + ``resume_early``, ``resume`` phases of system resume may have been + skipped for it). In that case, the ``->complete`` callback is entirely + responsible for putting the device into a consistent state after system + suspend if necessary. [For example, it may need to queue up a runtime + resume request for the device for this purpose.] To check if that is + the case, the ``->complete`` callback can consult the device's + ``power.direct_complete`` flag. Namely, if that flag is set when the + ``->complete`` callback is being run, it has been called directly after + the preceding ``->prepare`` and special actions may be required + to make the device work correctly afterward. + +At the end of these phases, drivers should be as functional as they were before +suspending: I/O can be performed using DMA and IRQs, and the relevant clocks are +gated on. + +However, the details here may again be platform-specific. For example, +some systems support multiple "run" states, and the mode in effect at +the end of resume might not be the one which preceded suspension. +That means availability of certain clocks or power supplies changed, +which could easily affect how a driver works. + +Drivers need to be able to handle hardware which has been reset since all of the +suspend methods were called, for example by complete reinitialization. +This may be the hardest part, and the one most protected by NDA'd documents +and chip errata. It's simplest if the hardware state hasn't changed since +the suspend was carried out, but that can only be guaranteed if the target +system sleep entered was suspend-to-idle. For the other system sleep states +that may not be the case (and usually isn't for ACPI-defined system sleep +states, like S3). + +Drivers must also be prepared to notice that the device has been removed +while the system was powered down, whenever that's physically possible. +PCMCIA, MMC, USB, Firewire, SCSI, and even IDE are common examples of busses +where common Linux platforms will see such removal. Details of how drivers +will notice and handle such removals are currently bus-specific, and often +involve a separate thread. + +These callbacks may return an error value, but the PM core will ignore such +errors since there's nothing it can do about them other than printing them in +the system log. + + +Entering Hibernation +-------------------- + +Hibernating the system is more complicated than putting it into sleep states, +because it involves creating and saving a system image. Therefore there are +more phases for hibernation, with a different set of callbacks. These phases +always run after tasks have been frozen and enough memory has been freed. + +The general procedure for hibernation is to quiesce all devices ("freeze"), +create an image of the system memory while everything is stable, reactivate all +devices ("thaw"), write the image to permanent storage, and finally shut down +the system ("power off"). The phases used to accomplish this are: ``prepare``, +``freeze``, ``freeze_late``, ``freeze_noirq``, ``thaw_noirq``, ``thaw_early``, +``thaw``, ``complete``, ``prepare``, ``poweroff``, ``poweroff_late``, +``poweroff_noirq``. + + 1. The ``prepare`` phase is discussed in the "Entering System Suspend" + section above. + + 2. The ``->freeze`` methods should quiesce the device so that it doesn't + generate IRQs or DMA, and they may need to save the values of device + registers. However the device does not have to be put in a low-power + state, and to save time it's best not to do so. Also, the device should + not be prepared to generate wakeup events. + + 3. The ``freeze_late`` phase is analogous to the ``suspend_late`` phase + described earlier, except that the device should not be put into a + low-power state and should not be allowed to generate wakeup events. + + 4. The ``freeze_noirq`` phase is analogous to the ``suspend_noirq`` phase + discussed earlier, except again that the device should not be put into + a low-power state and should not be allowed to generate wakeup events. + +At this point the system image is created. All devices should be inactive and +the contents of memory should remain undisturbed while this happens, so that the +image forms an atomic snapshot of the system state. + + 5. The ``thaw_noirq`` phase is analogous to the ``resume_noirq`` phase + discussed earlier. The main difference is that its methods can assume + the device is in the same state as at the end of the ``freeze_noirq`` + phase. + + 6. The ``thaw_early`` phase is analogous to the ``resume_early`` phase + described above. Its methods should undo the actions of the preceding + ``freeze_late``, if necessary. + + 7. The ``thaw`` phase is analogous to the ``resume`` phase discussed + earlier. Its methods should bring the device back to an operating + state, so that it can be used for saving the image if necessary. + + 8. The ``complete`` phase is discussed in the "Leaving System Suspend" + section above. + +At this point the system image is saved, and the devices then need to be +prepared for the upcoming system shutdown. This is much like suspending them +before putting the system into the suspend-to-idle, shallow or deep sleep state, +and the phases are similar. + + 9. The ``prepare`` phase is discussed above. + + 10. The ``poweroff`` phase is analogous to the ``suspend`` phase. + + 11. The ``poweroff_late`` phase is analogous to the ``suspend_late`` phase. + + 12. The ``poweroff_noirq`` phase is analogous to the ``suspend_noirq`` phase. + +The ``->poweroff``, ``->poweroff_late`` and ``->poweroff_noirq`` callbacks +should do essentially the same things as the ``->suspend``, ``->suspend_late`` +and ``->suspend_noirq`` callbacks, respectively. The only notable difference is +that they need not store the device register values, because the registers +should already have been stored during the ``freeze``, ``freeze_late`` or +``freeze_noirq`` phases. + + +Leaving Hibernation +------------------- + +Resuming from hibernation is, again, more complicated than resuming from a sleep +state in which the contents of main memory are preserved, because it requires +a system image to be loaded into memory and the pre-hibernation memory contents +to be restored before control can be passed back to the image kernel. + +Although in principle the image might be loaded into memory and the +pre-hibernation memory contents restored by the boot loader, in practice this +can't be done because boot loaders aren't smart enough and there is no +established protocol for passing the necessary information. So instead, the +boot loader loads a fresh instance of the kernel, called "the restore kernel", +into memory and passes control to it in the usual way. Then the restore kernel +reads the system image, restores the pre-hibernation memory contents, and passes +control to the image kernel. Thus two different kernel instances are involved +in resuming from hibernation. In fact, the restore kernel may be completely +different from the image kernel: a different configuration and even a different +version. This has important consequences for device drivers and their +subsystems. + +To be able to load the system image into memory, the restore kernel needs to +include at least a subset of device drivers allowing it to access the storage +medium containing the image, although it doesn't need to include all of the +drivers present in the image kernel. After the image has been loaded, the +devices managed by the boot kernel need to be prepared for passing control back +to the image kernel. This is very similar to the initial steps involved in +creating a system image, and it is accomplished in the same way, using +``prepare``, ``freeze``, and ``freeze_noirq`` phases. However, the devices +affected by these phases are only those having drivers in the restore kernel; +other devices will still be in whatever state the boot loader left them. + +Should the restoration of the pre-hibernation memory contents fail, the restore +kernel would go through the "thawing" procedure described above, using the +``thaw_noirq``, ``thaw_early``, ``thaw``, and ``complete`` phases, and then +continue running normally. This happens only rarely. Most often the +pre-hibernation memory contents are restored successfully and control is passed +to the image kernel, which then becomes responsible for bringing the system back +to the working state. + +To achieve this, the image kernel must restore the devices' pre-hibernation +functionality. The operation is much like waking up from a sleep state (with +the memory contents preserved), although it involves different phases: +``restore_noirq``, ``restore_early``, ``restore``, ``complete``. + + 1. The ``restore_noirq`` phase is analogous to the ``resume_noirq`` phase. + + 2. The ``restore_early`` phase is analogous to the ``resume_early`` phase. + + 3. The ``restore`` phase is analogous to the ``resume`` phase. + + 4. The ``complete`` phase is discussed above. + +The main difference from ``resume[_early|_noirq]`` is that +``restore[_early|_noirq]`` must assume the device has been accessed and +reconfigured by the boot loader or the restore kernel. Consequently, the state +of the device may be different from the state remembered from the ``freeze``, +``freeze_late`` and ``freeze_noirq`` phases. The device may even need to be +reset and completely re-initialized. In many cases this difference doesn't +matter, so the ``->resume[_early|_noirq]`` and ``->restore[_early|_norq]`` +method pointers can be set to the same routines. Nevertheless, different +callback pointers are used in case there is a situation where it actually does +matter. + + +Power Management Notifiers +========================== + +There are some operations that cannot be carried out by the power management +callbacks discussed above, because the callbacks occur too late or too early. +To handle these cases, subsystems and device drivers may register power +management notifiers that are called before tasks are frozen and after they have +been thawed. Generally speaking, the PM notifiers are suitable for performing +actions that either require user space to be available, or at least won't +interfere with user space. + +For details refer to :file:`Documentation/power/notifiers.txt`. + + +Device Low-Power (suspend) States +================================= + +Device low-power states aren't standard. One device might only handle +"on" and "off", while another might support a dozen different versions of +"on" (how many engines are active?), plus a state that gets back to "on" +faster than from a full "off". + +Some buses define rules about what different suspend states mean. PCI +gives one example: after the suspend sequence completes, a non-legacy +PCI device may not perform DMA or issue IRQs, and any wakeup events it +issues would be issued through the PME# bus signal. Plus, there are +several PCI-standard device states, some of which are optional. + +In contrast, integrated system-on-chip processors often use IRQs as the +wakeup event sources (so drivers would call :c:func:`enable_irq_wake`) and +might be able to treat DMA completion as a wakeup event (sometimes DMA can stay +active too, it'd only be the CPU and some peripherals that sleep). + +Some details here may be platform-specific. Systems may have devices that +can be fully active in certain sleep states, such as an LCD display that's +refreshed using DMA while most of the system is sleeping lightly ... and +its frame buffer might even be updated by a DSP or other non-Linux CPU while +the Linux control processor stays idle. + +Moreover, the specific actions taken may depend on the target system state. +One target system state might allow a given device to be very operational; +another might require a hard shut down with re-initialization on resume. +And two different target systems might use the same device in different +ways; the aforementioned LCD might be active in one product's "standby", +but a different product using the same SOC might work differently. + + +Device Power Management Domains +=============================== + +Sometimes devices share reference clocks or other power resources. In those +cases it generally is not possible to put devices into low-power states +individually. Instead, a set of devices sharing a power resource can be put +into a low-power state together at the same time by turning off the shared +power resource. Of course, they also need to be put into the full-power state +together, by turning the shared power resource on. A set of devices with this +property is often referred to as a power domain. A power domain may also be +nested inside another power domain. The nested domain is referred to as the +sub-domain of the parent domain. + +Support for power domains is provided through the :c:member:`pm_domain` field of +|struct| :c:type:`device`. This field is a pointer to an object of +type |struct| :c:type:`dev_pm_domain`, defined in :file:`include/linux/pm.h``, +providing a set of power management callbacks analogous to the subsystem-level +and device driver callbacks that are executed for the given device during all +power transitions, instead of the respective subsystem-level callbacks. +Specifically, if a device's :c:member:`pm_domain` pointer is not NULL, the +``->suspend()`` callback from the object pointed to by it will be executed +instead of its subsystem's (e.g. bus type's) ``->suspend()`` callback and +analogously for all of the remaining callbacks. In other words, power +management domain callbacks, if defined for the given device, always take +precedence over the callbacks provided by the device's subsystem (e.g. bus type). + +The support for device power management domains is only relevant to platforms +needing to use the same device driver power management callbacks in many +different power domain configurations and wanting to avoid incorporating the +support for power domains into subsystem-level callbacks, for example by +modifying the platform bus type. Other platforms need not implement it or take +it into account in any way. + +Devices may be defined as IRQ-safe which indicates to the PM core that their +runtime PM callbacks may be invoked with disabled interrupts (see +:file:`Documentation/power/runtime_pm.txt` for more information). If an +IRQ-safe device belongs to a PM domain, the runtime PM of the domain will be +disallowed, unless the domain itself is defined as IRQ-safe. However, it +makes sense to define a PM domain as IRQ-safe only if all the devices in it +are IRQ-safe. Moreover, if an IRQ-safe domain has a parent domain, the runtime +PM of the parent is only allowed if the parent itself is IRQ-safe too with the +additional restriction that all child domains of an IRQ-safe parent must also +be IRQ-safe. + + +Runtime Power Management +======================== + +Many devices are able to dynamically power down while the system is still +running. This feature is useful for devices that are not being used, and +can offer significant power savings on a running system. These devices +often support a range of runtime power states, which might use names such +as "off", "sleep", "idle", "active", and so on. Those states will in some +cases (like PCI) be partially constrained by the bus the device uses, and will +usually include hardware states that are also used in system sleep states. + +A system-wide power transition can be started while some devices are in low +power states due to runtime power management. The system sleep PM callbacks +should recognize such situations and react to them appropriately, but the +necessary actions are subsystem-specific. + +In some cases the decision may be made at the subsystem level while in other +cases the device driver may be left to decide. In some cases it may be +desirable to leave a suspended device in that state during a system-wide power +transition, but in other cases the device must be put back into the full-power +state temporarily, for example so that its system wakeup capability can be +disabled. This all depends on the hardware and the design of the subsystem and +device driver in question. + +During system-wide resume from a sleep state it's easiest to put devices into +the full-power state, as explained in :file:`Documentation/power/runtime_pm.txt`. +Refer to that document for more information regarding this particular issue as +well as for information on the device runtime power management framework in +general. diff --git a/Documentation/driver-api/pm/index.rst b/Documentation/driver-api/pm/index.rst new file mode 100644 index 000000000000..f7b3ce9e9ba0 --- /dev/null +++ b/Documentation/driver-api/pm/index.rst @@ -0,0 +1,15 @@ +======================= +Device Power Management +======================= + +.. toctree:: + + devices + types + +.. only:: subproject and html + + Indices + ======= + + * :ref:`genindex` diff --git a/Documentation/driver-api/pm/types.rst b/Documentation/driver-api/pm/types.rst new file mode 100644 index 000000000000..3ebdecc54104 --- /dev/null +++ b/Documentation/driver-api/pm/types.rst @@ -0,0 +1,5 @@ +================================== +Device Power Management Data Types +================================== + +.. kernel-doc:: include/linux/pm.h diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt deleted file mode 100644 index 73ddea39a9ce..000000000000 --- a/Documentation/power/devices.txt +++ /dev/null @@ -1,716 +0,0 @@ -Device Power Management - -Copyright (c) 2010-2011 Rafael J. Wysocki , Novell Inc. -Copyright (c) 2010 Alan Stern -Copyright (c) 2014 Intel Corp., Rafael J. Wysocki - - -Most of the code in Linux is device drivers, so most of the Linux power -management (PM) code is also driver-specific. Most drivers will do very -little; others, especially for platforms with small batteries (like cell -phones), will do a lot. - -This writeup gives an overview of how drivers interact with system-wide -power management goals, emphasizing the models and interfaces that are -shared by everything that hooks up to the driver model core. Read it as -background for the domain-specific work you'd do with any specific driver. - - -Two Models for Device Power Management -====================================== -Drivers will use one or both of these models to put devices into low-power -states: - - System Sleep model: - Drivers can enter low-power states as part of entering system-wide - low-power states like "suspend" (also known as "suspend-to-RAM"), or - (mostly for systems with disks) "hibernation" (also known as - "suspend-to-disk"). - - This is something that device, bus, and class drivers collaborate on - by implementing various role-specific suspend and resume methods to - cleanly power down hardware and software subsystems, then reactivate - them without loss of data. - - Some drivers can manage hardware wakeup events, which make the system - leave the low-power state. This feature may be enabled or disabled - using the relevant /sys/devices/.../power/wakeup file (for Ethernet - drivers the ioctl interface used by ethtool may also be used for this - purpose); enabling it may cost some power usage, but let the whole - system enter low-power states more often. - - Runtime Power Management model: - Devices may also be put into low-power states while the system is - running, independently of other power management activity in principle. - However, devices are not generally independent of each other (for - example, a parent device cannot be suspended unless all of its child - devices have been suspended). Moreover, depending on the bus type the - device is on, it may be necessary to carry out some bus-specific - operations on the device for this purpose. Devices put into low power - states at run time may require special handling during system-wide power - transitions (suspend or hibernation). - - For these reasons not only the device driver itself, but also the - appropriate subsystem (bus type, device type or device class) driver and - the PM core are involved in runtime power management. As in the system - sleep power management case, they need to collaborate by implementing - various role-specific suspend and resume methods, so that the hardware - is cleanly powered down and reactivated without data or service loss. - -There's not a lot to be said about those low-power states except that they are -very system-specific, and often device-specific. Also, that if enough devices -have been put into low-power states (at runtime), the effect may be very similar -to entering some system-wide low-power state (system sleep) ... and that -synergies exist, so that several drivers using runtime PM might put the system -into a state where even deeper power saving options are available. - -Most suspended devices will have quiesced all I/O: no more DMA or IRQs (except -for wakeup events), no more data read or written, and requests from upstream -drivers are no longer accepted. A given bus or platform may have different -requirements though. - -Examples of hardware wakeup events include an alarm from a real time clock, -network wake-on-LAN packets, keyboard or mouse activity, and media insertion -or removal (for PCMCIA, MMC/SD, USB, and so on). - - -Interfaces for Entering System Sleep States -=========================================== -There are programming interfaces provided for subsystems (bus type, device type, -device class) and device drivers to allow them to participate in the power -management of devices they are concerned with. These interfaces cover both -system sleep and runtime power management. - - -Device Power Management Operations ----------------------------------- -Device power management operations, at the subsystem level as well as at the -device driver level, are implemented by defining and populating objects of type -struct dev_pm_ops: - -struct dev_pm_ops { - int (*prepare)(struct device *dev); - void (*complete)(struct device *dev); - int (*suspend)(struct device *dev); - int (*resume)(struct device *dev); - int (*freeze)(struct device *dev); - int (*thaw)(struct device *dev); - int (*poweroff)(struct device *dev); - int (*restore)(struct device *dev); - int (*suspend_late)(struct device *dev); - int (*resume_early)(struct device *dev); - int (*freeze_late)(struct device *dev); - int (*thaw_early)(struct device *dev); - int (*poweroff_late)(struct device *dev); - int (*restore_early)(struct device *dev); - int (*suspend_noirq)(struct device *dev); - int (*resume_noirq)(struct device *dev); - int (*freeze_noirq)(struct device *dev); - int (*thaw_noirq)(struct device *dev); - int (*poweroff_noirq)(struct device *dev); - int (*restore_noirq)(struct device *dev); - int (*runtime_suspend)(struct device *dev); - int (*runtime_resume)(struct device *dev); - int (*runtime_idle)(struct device *dev); -}; - -This structure is defined in include/linux/pm.h and the methods included in it -are also described in that file. Their roles will be explained in what follows. -For now, it should be sufficient to remember that the last three methods are -specific to runtime power management while the remaining ones are used during -system-wide power transitions. - -There also is a deprecated "old" or "legacy" interface for power management -operations available at least for some subsystems. This approach does not use -struct dev_pm_ops objects and it is suitable only for implementing system sleep -power management methods. Therefore it is not described in this document, so -please refer directly to the source code for more information about it. - - -Subsystem-Level Methods ------------------------ -The core methods to suspend and resume devices reside in struct dev_pm_ops -pointed to by the ops member of struct dev_pm_domain, or by the pm member of -struct bus_type, struct device_type and struct class. They are mostly of -interest to the people writing infrastructure for platforms and buses, like PCI -or USB, or device type and device class drivers. They also are relevant to the -writers of device drivers whose subsystems (PM domains, device types, device -classes and bus types) don't provide all power management methods. - -Bus drivers implement these methods as appropriate for the hardware and the -drivers using it; PCI works differently from USB, and so on. Not many people -write subsystem-level drivers; most driver code is a "device driver" that builds -on top of bus-specific framework code. - -For more information on these driver calls, see the description later; -they are called in phases for every device, respecting the parent-child -sequencing in the driver model tree. - - -/sys/devices/.../power/wakeup files ------------------------------------ -All device objects in the driver model contain fields that control the handling -of system wakeup events (hardware signals that can force the system out of a -sleep state). These fields are initialized by bus or device driver code using -device_set_wakeup_capable() and device_set_wakeup_enable(), defined in -include/linux/pm_wakeup.h. - -The "power.can_wakeup" flag just records whether the device (and its driver) can -physically support wakeup events. The device_set_wakeup_capable() routine -affects this flag. The "power.wakeup" field is a pointer to an object of type -struct wakeup_source used for controlling whether or not the device should use -its system wakeup mechanism and for notifying the PM core of system wakeup -events signaled by the device. This object is only present for wakeup-capable -devices (i.e. devices whose "can_wakeup" flags are set) and is created (or -removed) by device_set_wakeup_capable(). - -Whether or not a device is capable of issuing wakeup events is a hardware -matter, and the kernel is responsible for keeping track of it. By contrast, -whether or not a wakeup-capable device should issue wakeup events is a policy -decision, and it is managed by user space through a sysfs attribute: the -"power/wakeup" file. User space can write the strings "enabled" or "disabled" -to it to indicate whether or not, respectively, the device is supposed to signal -system wakeup. This file is only present if the "power.wakeup" object exists -for the given device and is created (or removed) along with that object, by -device_set_wakeup_capable(). Reads from the file will return the corresponding -string. - -The "power/wakeup" file is supposed to contain the "disabled" string initially -for the majority of devices; the major exceptions are power buttons, keyboards, -and Ethernet adapters whose WoL (wake-on-LAN) feature has been set up with -ethtool. It should also default to "enabled" for devices that don't generate -wakeup requests on their own but merely forward wakeup requests from one bus to -another (like PCI Express ports). - -The device_may_wakeup() routine returns true only if the "power.wakeup" object -exists and the corresponding "power/wakeup" file contains the string "enabled". -This information is used by subsystems, like the PCI bus type code, to see -whether or not to enable the devices' wakeup mechanisms. If device wakeup -mechanisms are enabled or disabled directly by drivers, they also should use -device_may_wakeup() to decide what to do during a system sleep transition. -Device drivers, however, are not supposed to call device_set_wakeup_enable() -directly in any case. - -It ought to be noted that system wakeup is conceptually different from "remote -wakeup" used by runtime power management, although it may be supported by the -same physical mechanism. Remote wakeup is a feature allowing devices in -low-power states to trigger specific interrupts to signal conditions in which -they should be put into the full-power state. Those interrupts may or may not -be used to signal system wakeup events, depending on the hardware design. On -some systems it is impossible to trigger them from system sleep states. In any -case, remote wakeup should always be enabled for runtime power management for -all devices and drivers that support it. - -/sys/devices/.../power/control files ------------------------------------- -Each device in the driver model has a flag to control whether it is subject to -runtime power management. This flag, called runtime_auto, is initialized by the -bus type (or generally subsystem) code using pm_runtime_allow() or -pm_runtime_forbid(); the default is to allow runtime power management. - -The setting can be adjusted by user space by writing either "on" or "auto" to -the device's power/control sysfs file. Writing "auto" calls pm_runtime_allow(), -setting the flag and allowing the device to be runtime power-managed by its -driver. Writing "on" calls pm_runtime_forbid(), clearing the flag, returning -the device to full power if it was in a low-power state, and preventing the -device from being runtime power-managed. User space can check the current value -of the runtime_auto flag by reading the file. - -The device's runtime_auto flag has no effect on the handling of system-wide -power transitions. In particular, the device can (and in the majority of cases -should and will) be put into a low-power state during a system-wide transition -to a sleep state even though its runtime_auto flag is clear. - -For more information about the runtime power management framework, refer to -Documentation/power/runtime_pm.txt. - - -Calling Drivers to Enter and Leave System Sleep States -====================================================== -When the system goes into a sleep state, each device's driver is asked to -suspend the device by putting it into a state compatible with the target -system state. That's usually some version of "off", but the details are -system-specific. Also, wakeup-enabled devices will usually stay partly -functional in order to wake the system. - -When the system leaves that low-power state, the device's driver is asked to -resume it by returning it to full power. The suspend and resume operations -always go together, and both are multi-phase operations. - -For simple drivers, suspend might quiesce the device using class code -and then turn its hardware as "off" as possible during suspend_noirq. The -matching resume calls would then completely reinitialize the hardware -before reactivating its class I/O queues. - -More power-aware drivers might prepare the devices for triggering system wakeup -events. - - -Call Sequence Guarantees ------------------------- -To ensure that bridges and similar links needing to talk to a device are -available when the device is suspended or resumed, the device tree is -walked in a bottom-up order to suspend devices. A top-down order is -used to resume those devices. - -The ordering of the device tree is defined by the order in which devices -get registered: a child can never be registered, probed or resumed before -its parent; and can't be removed or suspended after that parent. - -The policy is that the device tree should match hardware bus topology. -(Or at least the control bus, for devices which use multiple busses.) -In particular, this means that a device registration may fail if the parent of -the device is suspending (i.e. has been chosen by the PM core as the next -device to suspend) or has already suspended, as well as after all of the other -devices have been suspended. Device drivers must be prepared to cope with such -situations. - - -System Power Management Phases ------------------------------- -Suspending or resuming the system is done in several phases. Different phases -are used for freeze, standby, and memory sleep states ("suspend-to-RAM") and the -hibernation state ("suspend-to-disk"). Each phase involves executing callbacks -for every device before the next phase begins. Not all busses or classes -support all these callbacks and not all drivers use all the callbacks. The -various phases always run after tasks have been frozen and before they are -unfrozen. Furthermore, the *_noirq phases run at a time when IRQ handlers have -been disabled (except for those marked with the IRQF_NO_SUSPEND flag). - -All phases use PM domain, bus, type, class or driver callbacks (that is, methods -defined in dev->pm_domain->ops, dev->bus->pm, dev->type->pm, dev->class->pm or -dev->driver->pm). These callbacks are regarded by the PM core as mutually -exclusive. Moreover, PM domain callbacks always take precedence over all of the -other callbacks and, for example, type callbacks take precedence over bus, class -and driver callbacks. To be precise, the following rules are used to determine -which callback to execute in the given phase: - - 1. If dev->pm_domain is present, the PM core will choose the callback - included in dev->pm_domain->ops for execution - - 2. Otherwise, if both dev->type and dev->type->pm are present, the callback - included in dev->type->pm will be chosen for execution. - - 3. Otherwise, if both dev->class and dev->class->pm are present, the - callback included in dev->class->pm will be chosen for execution. - - 4. Otherwise, if both dev->bus and dev->bus->pm are present, the callback - included in dev->bus->pm will be chosen for execution. - -This allows PM domains and device types to override callbacks provided by bus -types or device classes if necessary. - -The PM domain, type, class and bus callbacks may in turn invoke device- or -driver-specific methods stored in dev->driver->pm, but they don't have to do -that. - -If the subsystem callback chosen for execution is not present, the PM core will -execute the corresponding method from dev->driver->pm instead if there is one. - - -Entering System Suspend ------------------------ -When the system goes into the freeze, standby or memory sleep state, -the phases are: - - prepare, suspend, suspend_late, suspend_noirq. - - 1. The prepare phase is meant to prevent races by preventing new devices - from being registered; the PM core would never know that all the - children of a device had been suspended if new children could be - registered at will. (By contrast, devices may be unregistered at any - time.) Unlike the other suspend-related phases, during the prepare - phase the device tree is traversed top-down. - - After the prepare callback method returns, no new children may be - registered below the device. The method may also prepare the device or - driver in some way for the upcoming system power transition, but it - should not put the device into a low-power state. - - For devices supporting runtime power management, the return value of the - prepare callback can be used to indicate to the PM core that it may - safely leave the device in runtime suspend (if runtime-suspended - already), provided that all of the device's descendants are also left in - runtime suspend. Namely, if the prepare callback returns a positive - number and that happens for all of the descendants of the device too, - and all of them (including the device itself) are runtime-suspended, the - PM core will skip the suspend, suspend_late and suspend_noirq suspend - phases as well as the resume_noirq, resume_early and resume phases of - the following system resume for all of these devices. In that case, - the complete callback will be called directly after the prepare callback - and is entirely responsible for bringing the device back to the - functional state as appropriate. - - Note that this direct-complete procedure applies even if the device is - disabled for runtime PM; only the runtime-PM status matters. It follows - that if a device has system-sleep callbacks but does not support runtime - PM, then its prepare callback must never return a positive value. This - is because all devices are initially set to runtime-suspended with - runtime PM disabled. - - 2. The suspend methods should quiesce the device to stop it from performing - I/O. They also may save the device registers and put it into the - appropriate low-power state, depending on the bus type the device is on, - and they may enable wakeup events. - - 3 For a number of devices it is convenient to split suspend into the - "quiesce device" and "save device state" phases, in which cases - suspend_late is meant to do the latter. It is always executed after - runtime power management has been disabled for all devices. - - 4. The suspend_noirq phase occurs after IRQ handlers have been disabled, - which means that the driver's interrupt handler will not be called while - the callback method is running. The methods should save the values of - the device's registers that weren't saved previously and finally put the - device into the appropriate low-power state. - - The majority of subsystems and device drivers need not implement this - callback. However, bus types allowing devices to share interrupt - vectors, like PCI, generally need it; otherwise a driver might encounter - an error during the suspend phase by fielding a shared interrupt - generated by some other device after its own device had been set to low - power. - -At the end of these phases, drivers should have stopped all I/O transactions -(DMA, IRQs), saved enough state that they can re-initialize or restore previous -state (as needed by the hardware), and placed the device into a low-power state. -On many platforms they will gate off one or more clock sources; sometimes they -will also switch off power supplies or reduce voltages. (Drivers supporting -runtime PM may already have performed some or all of these steps.) - -If device_may_wakeup(dev) returns true, the device should be prepared for -generating hardware wakeup signals to trigger a system wakeup event when the -system is in the sleep state. For example, enable_irq_wake() might identify -GPIO signals hooked up to a switch or other external hardware, and -pci_enable_wake() does something similar for the PCI PME signal. - -If any of these callbacks returns an error, the system won't enter the desired -low-power state. Instead the PM core will unwind its actions by resuming all -the devices that were suspended. - - -Leaving System Suspend ----------------------- -When resuming from freeze, standby or memory sleep, the phases are: - - resume_noirq, resume_early, resume, complete. - - 1. The resume_noirq callback methods should perform any actions needed - before the driver's interrupt handlers are invoked. This generally - means undoing the actions of the suspend_noirq phase. If the bus type - permits devices to share interrupt vectors, like PCI, the method should - bring the device and its driver into a state in which the driver can - recognize if the device is the source of incoming interrupts, if any, - and handle them correctly. - - For example, the PCI bus type's ->pm.resume_noirq() puts the device into - the full-power state (D0 in the PCI terminology) and restores the - standard configuration registers of the device. Then it calls the - device driver's ->pm.resume_noirq() method to perform device-specific - actions. - - 2. The resume_early methods should prepare devices for the execution of - the resume methods. This generally involves undoing the actions of the - preceding suspend_late phase. - - 3 The resume methods should bring the device back to its operating - state, so that it can perform normal I/O. This generally involves - undoing the actions of the suspend phase. - - 4. The complete phase should undo the actions of the prepare phase. Note, - however, that new children may be registered below the device as soon as - the resume callbacks occur; it's not necessary to wait until the - complete phase. - - Moreover, if the preceding prepare callback returned a positive number, - the device may have been left in runtime suspend throughout the whole - system suspend and resume (the suspend, suspend_late, suspend_noirq - phases of system suspend and the resume_noirq, resume_early, resume - phases of system resume may have been skipped for it). In that case, - the complete callback is entirely responsible for bringing the device - back to the functional state after system suspend if necessary. [For - example, it may need to queue up a runtime resume request for the device - for this purpose.] To check if that is the case, the complete callback - can consult the device's power.direct_complete flag. Namely, if that - flag is set when the complete callback is being run, it has been called - directly after the preceding prepare and special action may be required - to make the device work correctly afterward. - -At the end of these phases, drivers should be as functional as they were before -suspending: I/O can be performed using DMA and IRQs, and the relevant clocks are -gated on. - -However, the details here may again be platform-specific. For example, -some systems support multiple "run" states, and the mode in effect at -the end of resume might not be the one which preceded suspension. -That means availability of certain clocks or power supplies changed, -which could easily affect how a driver works. - -Drivers need to be able to handle hardware which has been reset since the -suspend methods were called, for example by complete reinitialization. -This may be the hardest part, and the one most protected by NDA'd documents -and chip errata. It's simplest if the hardware state hasn't changed since -the suspend was carried out, but that can't be guaranteed (in fact, it usually -is not the case). - -Drivers must also be prepared to notice that the device has been removed -while the system was powered down, whenever that's physically possible. -PCMCIA, MMC, USB, Firewire, SCSI, and even IDE are common examples of busses -where common Linux platforms will see such removal. Details of how drivers -will notice and handle such removals are currently bus-specific, and often -involve a separate thread. - -These callbacks may return an error value, but the PM core will ignore such -errors since there's nothing it can do about them other than printing them in -the system log. - - -Entering Hibernation --------------------- -Hibernating the system is more complicated than putting it into the other -sleep states, because it involves creating and saving a system image. -Therefore there are more phases for hibernation, with a different set of -callbacks. These phases always run after tasks have been frozen and memory has -been freed. - -The general procedure for hibernation is to quiesce all devices (freeze), create -an image of the system memory while everything is stable, reactivate all -devices (thaw), write the image to permanent storage, and finally shut down the -system (poweroff). The phases used to accomplish this are: - - prepare, freeze, freeze_late, freeze_noirq, thaw_noirq, thaw_early, - thaw, complete, prepare, poweroff, poweroff_late, poweroff_noirq - - 1. The prepare phase is discussed in the "Entering System Suspend" section - above. - - 2. The freeze methods should quiesce the device so that it doesn't generate - IRQs or DMA, and they may need to save the values of device registers. - However the device does not have to be put in a low-power state, and to - save time it's best not to do so. Also, the device should not be - prepared to generate wakeup events. - - 3. The freeze_late phase is analogous to the suspend_late phase described - above, except that the device should not be put in a low-power state and - should not be allowed to generate wakeup events by it. - - 4. The freeze_noirq phase is analogous to the suspend_noirq phase discussed - above, except again that the device should not be put in a low-power - state and should not be allowed to generate wakeup events. - -At this point the system image is created. All devices should be inactive and -the contents of memory should remain undisturbed while this happens, so that the -image forms an atomic snapshot of the system state. - - 5. The thaw_noirq phase is analogous to the resume_noirq phase discussed - above. The main difference is that its methods can assume the device is - in the same state as at the end of the freeze_noirq phase. - - 6. The thaw_early phase is analogous to the resume_early phase described - above. Its methods should undo the actions of the preceding - freeze_late, if necessary. - - 7. The thaw phase is analogous to the resume phase discussed above. Its - methods should bring the device back to an operating state, so that it - can be used for saving the image if necessary. - - 8. The complete phase is discussed in the "Leaving System Suspend" section - above. - -At this point the system image is saved, and the devices then need to be -prepared for the upcoming system shutdown. This is much like suspending them -before putting the system into the freeze, standby or memory sleep state, -and the phases are similar. - - 9. The prepare phase is discussed above. - - 10. The poweroff phase is analogous to the suspend phase. - - 11. The poweroff_late phase is analogous to the suspend_late phase. - - 12. The poweroff_noirq phase is analogous to the suspend_noirq phase. - -The poweroff, poweroff_late and poweroff_noirq callbacks should do essentially -the same things as the suspend, suspend_late and suspend_noirq callbacks, -respectively. The only notable difference is that they need not store the -device register values, because the registers should already have been stored -during the freeze, freeze_late or freeze_noirq phases. - - -Leaving Hibernation -------------------- -Resuming from hibernation is, again, more complicated than resuming from a sleep -state in which the contents of main memory are preserved, because it requires -a system image to be loaded into memory and the pre-hibernation memory contents -to be restored before control can be passed back to the image kernel. - -Although in principle, the image might be loaded into memory and the -pre-hibernation memory contents restored by the boot loader, in practice this -can't be done because boot loaders aren't smart enough and there is no -established protocol for passing the necessary information. So instead, the -boot loader loads a fresh instance of the kernel, called the boot kernel, into -memory and passes control to it in the usual way. Then the boot kernel reads -the system image, restores the pre-hibernation memory contents, and passes -control to the image kernel. Thus two different kernels are involved in -resuming from hibernation. In fact, the boot kernel may be completely different -from the image kernel: a different configuration and even a different version. -This has important consequences for device drivers and their subsystems. - -To be able to load the system image into memory, the boot kernel needs to -include at least a subset of device drivers allowing it to access the storage -medium containing the image, although it doesn't need to include all of the -drivers present in the image kernel. After the image has been loaded, the -devices managed by the boot kernel need to be prepared for passing control back -to the image kernel. This is very similar to the initial steps involved in -creating a system image, and it is accomplished in the same way, using prepare, -freeze, and freeze_noirq phases. However the devices affected by these phases -are only those having drivers in the boot kernel; other devices will still be in -whatever state the boot loader left them. - -Should the restoration of the pre-hibernation memory contents fail, the boot -kernel would go through the "thawing" procedure described above, using the -thaw_noirq, thaw, and complete phases, and then continue running normally. This -happens only rarely. Most often the pre-hibernation memory contents are -restored successfully and control is passed to the image kernel, which then -becomes responsible for bringing the system back to the working state. - -To achieve this, the image kernel must restore the devices' pre-hibernation -functionality. The operation is much like waking up from the memory sleep -state, although it involves different phases: - - restore_noirq, restore_early, restore, complete - - 1. The restore_noirq phase is analogous to the resume_noirq phase. - - 2. The restore_early phase is analogous to the resume_early phase. - - 3. The restore phase is analogous to the resume phase. - - 4. The complete phase is discussed above. - -The main difference from resume[_early|_noirq] is that restore[_early|_noirq] -must assume the device has been accessed and reconfigured by the boot loader or -the boot kernel. Consequently the state of the device may be different from the -state remembered from the freeze, freeze_late and freeze_noirq phases. The -device may even need to be reset and completely re-initialized. In many cases -this difference doesn't matter, so the resume[_early|_noirq] and -restore[_early|_norq] method pointers can be set to the same routines. -Nevertheless, different callback pointers are used in case there is a situation -where it actually does matter. - - -Device Power Management Domains -------------------------------- -Sometimes devices share reference clocks or other power resources. In those -cases it generally is not possible to put devices into low-power states -individually. Instead, a set of devices sharing a power resource can be put -into a low-power state together at the same time by turning off the shared -power resource. Of course, they also need to be put into the full-power state -together, by turning the shared power resource on. A set of devices with this -property is often referred to as a power domain. A power domain may also be -nested inside another power domain. The nested domain is referred to as the -sub-domain of the parent domain. - -Support for power domains is provided through the pm_domain field of struct -device. This field is a pointer to an object of type struct dev_pm_domain, -defined in include/linux/pm.h, providing a set of power management callbacks -analogous to the subsystem-level and device driver callbacks that are executed -for the given device during all power transitions, instead of the respective -subsystem-level callbacks. Specifically, if a device's pm_domain pointer is -not NULL, the ->suspend() callback from the object pointed to by it will be -executed instead of its subsystem's (e.g. bus type's) ->suspend() callback and -analogously for all of the remaining callbacks. In other words, power -management domain callbacks, if defined for the given device, always take -precedence over the callbacks provided by the device's subsystem (e.g. bus -type). - -The support for device power management domains is only relevant to platforms -needing to use the same device driver power management callbacks in many -different power domain configurations and wanting to avoid incorporating the -support for power domains into subsystem-level callbacks, for example by -modifying the platform bus type. Other platforms need not implement it or take -it into account in any way. - -Devices may be defined as IRQ-safe which indicates to the PM core that their -runtime PM callbacks may be invoked with disabled interrupts (see -Documentation/power/runtime_pm.txt for more information). If an IRQ-safe -device belongs to a PM domain, the runtime PM of the domain will be -disallowed, unless the domain itself is defined as IRQ-safe. However, it -makes sense to define a PM domain as IRQ-safe only if all the devices in it -are IRQ-safe. Moreover, if an IRQ-safe domain has a parent domain, the runtime -PM of the parent is only allowed if the parent itself is IRQ-safe too with the -additional restriction that all child domains of an IRQ-safe parent must also -be IRQ-safe. - -Device Low Power (suspend) States ---------------------------------- -Device low-power states aren't standard. One device might only handle -"on" and "off", while another might support a dozen different versions of -"on" (how many engines are active?), plus a state that gets back to "on" -faster than from a full "off". - -Some busses define rules about what different suspend states mean. PCI -gives one example: after the suspend sequence completes, a non-legacy -PCI device may not perform DMA or issue IRQs, and any wakeup events it -issues would be issued through the PME# bus signal. Plus, there are -several PCI-standard device states, some of which are optional. - -In contrast, integrated system-on-chip processors often use IRQs as the -wakeup event sources (so drivers would call enable_irq_wake) and might -be able to treat DMA completion as a wakeup event (sometimes DMA can stay -active too, it'd only be the CPU and some peripherals that sleep). - -Some details here may be platform-specific. Systems may have devices that -can be fully active in certain sleep states, such as an LCD display that's -refreshed using DMA while most of the system is sleeping lightly ... and -its frame buffer might even be updated by a DSP or other non-Linux CPU while -the Linux control processor stays idle. - -Moreover, the specific actions taken may depend on the target system state. -One target system state might allow a given device to be very operational; -another might require a hard shut down with re-initialization on resume. -And two different target systems might use the same device in different -ways; the aforementioned LCD might be active in one product's "standby", -but a different product using the same SOC might work differently. - - -Power Management Notifiers --------------------------- -There are some operations that cannot be carried out by the power management -callbacks discussed above, because the callbacks occur too late or too early. -To handle these cases, subsystems and device drivers may register power -management notifiers that are called before tasks are frozen and after they have -been thawed. Generally speaking, the PM notifiers are suitable for performing -actions that either require user space to be available, or at least won't -interfere with user space. - -For details refer to Documentation/power/notifiers.txt. - - -Runtime Power Management -======================== -Many devices are able to dynamically power down while the system is still -running. This feature is useful for devices that are not being used, and -can offer significant power savings on a running system. These devices -often support a range of runtime power states, which might use names such -as "off", "sleep", "idle", "active", and so on. Those states will in some -cases (like PCI) be partially constrained by the bus the device uses, and will -usually include hardware states that are also used in system sleep states. - -A system-wide power transition can be started while some devices are in low -power states due to runtime power management. The system sleep PM callbacks -should recognize such situations and react to them appropriately, but the -necessary actions are subsystem-specific. - -In some cases the decision may be made at the subsystem level while in other -cases the device driver may be left to decide. In some cases it may be -desirable to leave a suspended device in that state during a system-wide power -transition, but in other cases the device must be put back into the full-power -state temporarily, for example so that its system wakeup capability can be -disabled. This all depends on the hardware and the design of the subsystem and -device driver in question. - -During system-wide resume from a sleep state it's easiest to put devices into -the full-power state, as explained in Documentation/power/runtime_pm.txt. Refer -to that document for more information regarding this particular issue as well as -for information on the device runtime power management framework in general. diff --git a/include/linux/pm.h b/include/linux/pm.h index 10867b11d503..a0894bc52bb4 100644 --- a/include/linux/pm.h +++ b/include/linux/pm.h @@ -276,9 +276,6 @@ typedef struct pm_message { * example, if it detects that a child was unplugged while the system was * asleep). * - * Refer to Documentation/power/devices.txt for more information about the role - * of the above callbacks in the system suspend process. - * * There also are callbacks related to runtime power management of devices. * Again, as a rule these callbacks are executed by the PM core for subsystems * (PM domains, device types, classes and bus types) and the subsystem-level -- cgit v1.2.3 From 730c4c053012b058ccb5393bbc1691e4e872e741 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Thu, 2 Feb 2017 01:38:54 +0100 Subject: PM / sleep / docs: Convert PM notifiers document to reST Move the document describing PM notifiers (used during system sleep state transitions) to Documentation/driver-api/pm/, convert it to reST and update it to use current terminology. Also replace the remaining references to the old version of it in .txt documents with references to the new one. Signed-off-by: Rafael J. Wysocki Signed-off-by: Jonathan Corbet --- Documentation/driver-api/pm/devices.rst | 2 +- Documentation/driver-api/pm/index.rst | 1 + Documentation/driver-api/pm/notifiers.rst | 70 +++++++++++++++++++++++++++++++ Documentation/power/00-INDEX | 2 - Documentation/power/freezing-of-tasks.txt | 3 +- Documentation/power/notifiers.txt | 55 ------------------------ Documentation/power/pci.txt | 2 +- 7 files changed, 75 insertions(+), 60 deletions(-) create mode 100644 Documentation/driver-api/pm/notifiers.rst delete mode 100644 Documentation/power/notifiers.txt (limited to 'Documentation') diff --git a/Documentation/driver-api/pm/devices.rst b/Documentation/driver-api/pm/devices.rst index f165cf6f733e..0e8cf4efd7e7 100644 --- a/Documentation/driver-api/pm/devices.rst +++ b/Documentation/driver-api/pm/devices.rst @@ -620,7 +620,7 @@ been thawed. Generally speaking, the PM notifiers are suitable for performing actions that either require user space to be available, or at least won't interfere with user space. -For details refer to :file:`Documentation/power/notifiers.txt`. +For details refer to :doc:`notifiers`. Device Low-Power (suspend) States diff --git a/Documentation/driver-api/pm/index.rst b/Documentation/driver-api/pm/index.rst index f7b3ce9e9ba0..2f6d0e9cf6b7 100644 --- a/Documentation/driver-api/pm/index.rst +++ b/Documentation/driver-api/pm/index.rst @@ -5,6 +5,7 @@ Device Power Management .. toctree:: devices + notifiers types .. only:: subproject and html diff --git a/Documentation/driver-api/pm/notifiers.rst b/Documentation/driver-api/pm/notifiers.rst new file mode 100644 index 000000000000..62f860026992 --- /dev/null +++ b/Documentation/driver-api/pm/notifiers.rst @@ -0,0 +1,70 @@ +============================= +Suspend/Hibernation Notifiers +============================= + +:: + + Copyright (c) 2016 Intel Corp., Rafael J. Wysocki + +There are some operations that subsystems or drivers may want to carry out +before hibernation/suspend or after restore/resume, but they require the system +to be fully functional, so the drivers' and subsystems' ``->suspend()`` and +``->resume()`` or even ``->prepare()`` and ``->complete()`` callbacks are not +suitable for this purpose. + +For example, device drivers may want to upload firmware to their devices after +resume/restore, but they cannot do it by calling :c:func:`request_firmware()` +from their ``->resume()`` or ``->complete()`` callback routines (user land +processes are frozen at these points). The solution may be to load the firmware +into memory before processes are frozen and upload it from there in the +``->resume()`` routine. A suspend/hibernation notifier may be used for that. + +Subsystems or drivers having such needs can register suspend notifiers that +will be called upon the following events by the PM core: + +``PM_HIBERNATION_PREPARE`` + The system is going to hibernate, tasks will be frozen immediately. This + is different from ``PM_SUSPEND_PREPARE`` below, because in this case + additional work is done between the notifiers and the invocation of PM + callbacks for the "freeze" transition. + +``PM_POST_HIBERNATION`` + The system memory state has been restored from a hibernation image or an + error occurred during hibernation. Device restore callbacks have been + executed and tasks have been thawed. + +``PM_RESTORE_PREPARE`` + The system is going to restore a hibernation image. If all goes well, + the restored image kernel will issue a ``PM_POST_HIBERNATION`` + notification. + +``PM_POST_RESTORE`` + An error occurred during restore from hibernation. Device restore + callbacks have been executed and tasks have been thawed. + +``PM_SUSPEND_PREPARE`` + The system is preparing for suspend. + +``PM_POST_SUSPEND`` + The system has just resumed or an error occurred during suspend. Device + resume callbacks have been executed and tasks have been thawed. + +It is generally assumed that whatever the notifiers do for +``PM_HIBERNATION_PREPARE``, should be undone for ``PM_POST_HIBERNATION``. +Analogously, operations carried out for ``PM_SUSPEND_PREPARE`` should be +reversed for ``PM_POST_SUSPEND``. + +Moreover, if one of the notifiers fails for the ``PM_HIBERNATION_PREPARE`` or +``PM_SUSPEND_PREPARE`` event, the notifiers that have already succeeded for that +event will be called for ``PM_POST_HIBERNATION`` or ``PM_POST_SUSPEND``, +respectively. + +The hibernation and suspend notifiers are called with :c:data:`pm_mutex` held. +They are defined in the usual way, but their last argument is meaningless (it is +always NULL). + +To register and/or unregister a suspend notifier use +:c:func:`register_pm_notifier()` and :c:func:`unregister_pm_notifier()`, +respectively (both defined in :file:`include/linux/suspend.h`). If you don't +need to unregister the notifier, you can also use the :c:func:`pm_notifier()` +macro defined in :file:`include/linux/suspend.h`. diff --git a/Documentation/power/00-INDEX b/Documentation/power/00-INDEX index 7cb6085839f3..7f3c2def2cac 100644 --- a/Documentation/power/00-INDEX +++ b/Documentation/power/00-INDEX @@ -14,8 +14,6 @@ freezing-of-tasks.txt - How processes and controlled during suspend interface.txt - Power management user interface in /sys/power -notifiers.txt - - Registering suspend notifiers in device drivers opp.txt - Operating Performance Point library pci.txt diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index 85894d83b352..af005770e767 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -197,7 +197,8 @@ tasks, since it generally exists anyway. A driver must have all firmwares it may need in RAM before suspend() is called. If keeping them is not practical, for example due to their size, they must be -requested early enough using the suspend notifier API described in notifiers.txt. +requested early enough using the suspend notifier API described in +Documentation/driver-api/pm/notifiers.rst. VI. Are there any precautions to be taken to prevent freezing failures? diff --git a/Documentation/power/notifiers.txt b/Documentation/power/notifiers.txt deleted file mode 100644 index a81fa254303d..000000000000 --- a/Documentation/power/notifiers.txt +++ /dev/null @@ -1,55 +0,0 @@ -Suspend notifiers - (C) 2007-2011 Rafael J. Wysocki , GPL - -There are some operations that subsystems or drivers may want to carry out -before hibernation/suspend or after restore/resume, but they require the system -to be fully functional, so the drivers' and subsystems' .suspend() and .resume() -or even .prepare() and .complete() callbacks are not suitable for this purpose. -For example, device drivers may want to upload firmware to their devices after -resume/restore, but they cannot do it by calling request_firmware() from their -.resume() or .complete() routines (user land processes are frozen at these -points). The solution may be to load the firmware into memory before processes -are frozen and upload it from there in the .resume() routine. -A suspend/hibernation notifier may be used for this purpose. - -The subsystems or drivers having such needs can register suspend notifiers that -will be called upon the following events by the PM core: - -PM_HIBERNATION_PREPARE The system is going to hibernate, tasks will be frozen - immediately. This is different from PM_SUSPEND_PREPARE - below because here we do additional work between notifiers - and drivers freezing. - -PM_POST_HIBERNATION The system memory state has been restored from a - hibernation image or an error occurred during - hibernation. Device drivers' restore callbacks have - been executed and tasks have been thawed. - -PM_RESTORE_PREPARE The system is going to restore a hibernation image. - If all goes well, the restored kernel will issue a - PM_POST_HIBERNATION notification. - -PM_POST_RESTORE An error occurred during restore from hibernation. - Device drivers' restore callbacks have been executed - and tasks have been thawed. - -PM_SUSPEND_PREPARE The system is preparing for suspend. - -PM_POST_SUSPEND The system has just resumed or an error occurred during - suspend. Device drivers' resume callbacks have been - executed and tasks have been thawed. - -It is generally assumed that whatever the notifiers do for -PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION. Analogously, -operations performed for PM_SUSPEND_PREPARE should be reversed for -PM_POST_SUSPEND. Additionally, all of the notifiers are called for -PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and -all of the notifiers are called for PM_POST_SUSPEND if one of them fails for -PM_SUSPEND_PREPARE. - -The hibernation and suspend notifiers are called with pm_mutex held. They are -defined in the usual way, but their last argument is meaningless (it is always -NULL). To register and/or unregister a suspend notifier use the functions -register_pm_notifier() and unregister_pm_notifier(), respectively, defined in -include/linux/suspend.h . If you don't need to unregister the notifier, you can -also use the pm_notifier() macro defined in include/linux/suspend.h . diff --git a/Documentation/power/pci.txt b/Documentation/power/pci.txt index 85c746cbab2c..a1b7f7158930 100644 --- a/Documentation/power/pci.txt +++ b/Documentation/power/pci.txt @@ -713,7 +713,7 @@ In addition to that the prepare() callback may carry out some operations preparing the device to be suspended, although it should not allocate memory (if additional memory is required to suspend the device, it has to be preallocated earlier, for example in a suspend/hibernate notifier as described -in Documentation/power/notifiers.txt). +in Documentation/driver-api/pm/notifiers.rst). 3.1.2. suspend() -- cgit v1.2.3 From 2185d4df8a50ba771d2f9cbd7d7b74c0e70aa1db Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Mon, 6 Feb 2017 11:35:20 -0700 Subject: docs: Fix a warning in the Korean HOWTO.rst translation An extra space in the wrong place made Sphinx unhappy; take it out. Signed-off-by: Jonathan Corbet --- Documentation/translations/ko_KR/howto.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/translations/ko_KR/howto.rst b/Documentation/translations/ko_KR/howto.rst index 3b0c15b277e0..2333697251dd 100644 --- a/Documentation/translations/ko_KR/howto.rst +++ b/Documentation/translations/ko_KR/howto.rst @@ -289,8 +289,8 @@ pub/linux/kernel/v4.x/ 디렉토리에서 참조될 수 있다.개발 프로세 Andrew Morton의 글이 있다. *"커널이 언제 배포될지는 아무도 모른다. 왜냐하면 배포는 알려진 - 버그의 상황에 따라 배포되는 것이지 미리정해 놓은 시간에 따라 - 배포되는 것은 아니기 때문이다."* + 버그의 상황에 따라 배포되는 것이지 미리정해 놓은 시간에 따라 + 배포되는 것은 아니기 때문이다."* 4.x.y - 안정 커널 트리 ~~~~~~~~~~~~~~~~~~~~~~ -- cgit v1.2.3 From dc36143fba936d8f1a673e2b554bc5b6cb0dd9ce Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Mon, 6 Feb 2017 11:52:19 -0700 Subject: docs: Remove the copyright year from conf.py It had gone stale, of course, as it would every year, a single date doesn't really cover things, and the date isn't really needed anyway. --- Documentation/conf.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/conf.py b/Documentation/conf.py index 1ac958c0333d..f6823cf01275 100644 --- a/Documentation/conf.py +++ b/Documentation/conf.py @@ -58,7 +58,7 @@ master_doc = 'index' # General information about the project. project = 'The Linux Kernel' -copyright = '2016, The kernel development community' +copyright = 'The kernel development community' author = 'The kernel development community' # The version info for the project you're documenting, acts as replacement for -- cgit v1.2.3 From da23e4d16ded49ac648fa78c45aa327d4b8ed522 Mon Sep 17 00:00:00 2001 From: Martin Kepplinger Date: Thu, 9 Feb 2017 07:53:29 +0100 Subject: Documentation: input: fix path to input code definitions The UAPI header split failed to update the documentation for the input event codes; fix things accordingly. Signed-off-by: Martin Kepplinger Signed-off-by: Jonathan Corbet --- Documentation/input/input.txt | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/input/input.txt b/Documentation/input/input.txt index 0acfddbe2028..7ebce100fe90 100644 --- a/Documentation/input/input.txt +++ b/Documentation/input/input.txt @@ -279,10 +279,10 @@ struct input_event { 'time' is the timestamp, it returns the time at which the event happened. Type is for example EV_REL for relative moment, EV_KEY for a keypress or -release. More types are defined in include/linux/input.h. +release. More types are defined in include/uapi/linux/input-event-codes.h. 'code' is event code, for example REL_X or KEY_BACKSPACE, again a complete -list is in include/linux/input.h. +list is in include/uapi/linux/input-event-codes.h. 'value' is the value the event carries. Either a relative change for EV_REL, absolute new value for EV_ABS (joysticks ...), or 0 for EV_KEY for -- cgit v1.2.3 From 9210501f475a2f33e59254bcae5fd1542b64f421 Mon Sep 17 00:00:00 2001 From: Nathan Howard Date: Thu, 9 Feb 2017 18:36:36 -0500 Subject: Documentation: DMA-ISA-LPC.txt Fixed spelling issue. Signed-off-by: Nathan Howard Signed-off-by: Jonathan Corbet --- Documentation/DMA-ISA-LPC.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/DMA-ISA-LPC.txt b/Documentation/DMA-ISA-LPC.txt index b1a19835e907..c41331398752 100644 --- a/Documentation/DMA-ISA-LPC.txt +++ b/Documentation/DMA-ISA-LPC.txt @@ -42,7 +42,7 @@ requirements you pass the flag GFP_DMA to kmalloc. Unfortunately the memory available for ISA DMA is scarce so unless you allocate the memory during boot-up it's a good idea to also pass -__GFP_REPEAT and __GFP_NOWARN to make the allocater try a bit harder. +__GFP_REPEAT and __GFP_NOWARN to make the allocator try a bit harder. (This scarcity also means that you should allocate the buffer as early as possible and not release it until the driver is unloaded.) -- cgit v1.2.3 From c33dea1eda7159f6854dcb54e58906936c26e727 Mon Sep 17 00:00:00 2001 From: Jim Davis Date: Fri, 10 Feb 2017 17:06:50 -0700 Subject: Documentation: make Makefile.sphinx no-ops quieter Silence the "make[1]: Nothing to be done for ..." messages for the no-op targets in Makefile.sphinx. Signed-off-by: Jim Davis Signed-off-by: Jonathan Corbet --- Documentation/Makefile.sphinx | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation') diff --git a/Documentation/Makefile.sphinx b/Documentation/Makefile.sphinx index 48b2b0241a3a..8284f3d1b022 100644 --- a/Documentation/Makefile.sphinx +++ b/Documentation/Makefile.sphinx @@ -98,9 +98,13 @@ endif # HAVE_SPHINX # no-ops for the Sphinx toolchain sgmldocs: + @: psdocs: + @: mandocs: + @: installmandocs: + @: cleandocs: $(Q)rm -rf $(BUILDDIR) -- cgit v1.2.3 From 291b9d73681f3e0123b8954eb20be22342987afc Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Mon, 13 Feb 2017 11:16:02 -0800 Subject: Improve sparse documentation Add documentation of -DCONFIG_SPARSE_RCU_POINTER. I started to add documentation of -D__CHECK_ENDIAN__ as well, but discovered I'm too late; that's now enabled by default. Signed-off-by: Matthew Wilcox Signed-off-by: Jonathan Corbet --- Documentation/dev-tools/sparse.rst | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'Documentation') diff --git a/Documentation/dev-tools/sparse.rst b/Documentation/dev-tools/sparse.rst index 78aa00a604a0..ffdcc97f6f5a 100644 --- a/Documentation/dev-tools/sparse.rst +++ b/Documentation/dev-tools/sparse.rst @@ -103,3 +103,9 @@ have already built it. The optional make variable CF can be used to pass arguments to sparse. The build system passes -Wbitwise to sparse automatically. + +Checking RCU annotations +~~~~~~~~~~~~~~~~~~~~~~~~ + +RCU annotations are not checked by default. To enable RCU annotation +checks, include -DCONFIG_SPARSE_RCU_POINTER in your CF flags. -- cgit v1.2.3 From 0f3a249110bea205b025a108f4b360c1d2ff8880 Mon Sep 17 00:00:00 2001 From: Jim Davis Date: Mon, 13 Feb 2017 17:02:57 -0700 Subject: Documentation: DocBook/Makefile comment typo Fix a se for so typo. Signed-off-by: Jim Davis Signed-off-by: Jonathan Corbet --- Documentation/DocBook/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index c95b1aa47b45..327bf57f4599 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -272,6 +272,6 @@ cleandocs: $(Q)rm -rf $(call objectify, $(clean-dirs)) # Declare the contents of the .PHONY variable as phony. We keep that -# information in a variable se we can use it in if_changed and friends. +# information in a variable so we can use it in if_changed and friends. .PHONY: $(PHONY) -- cgit v1.2.3 From 72f8f677e3ec685865392846c356e08771d49f13 Mon Sep 17 00:00:00 2001 From: Tyler Hicks Date: Tue, 14 Feb 2017 04:04:17 +0000 Subject: Documentation: Fix linux-api list typo A Japanese translation file contained the incorrect email address for the linux-api list. Signed-off-by: Tyler Hicks Signed-off-by: Jonathan Corbet --- Documentation/translations/ja_JP/HOWTO | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/translations/ja_JP/HOWTO b/Documentation/translations/ja_JP/HOWTO index b03fc8047f03..4ebd20750ef1 100644 --- a/Documentation/translations/ja_JP/HOWTO +++ b/Documentation/translations/ja_JP/HOWTO @@ -111,7 +111,7 @@ Linux カーネルソースツリーは幅広い範囲のドキュメントを カーネルの変更が、カーネルがユーザ空間に公開しているインターフェイスの 変更を引き起こす場合、その変更を説明するマニュアルページのパッチや情報 をマニュアルページのメンテナ mtk.manpages@gmail.com に送り、CC を -linux-api@ver.kernel.org に送ることを勧めます。 +linux-api@vger.kernel.org に送ることを勧めます。 以下はカーネルソースツリーに含まれている読んでおくべきファイルの一覧で す- -- cgit v1.2.3 From 62924fd789c6a381b772141f78a82361f46ae397 Mon Sep 17 00:00:00 2001 From: Rémy Léone Date: Wed, 15 Feb 2017 13:16:35 +0100 Subject: Add a target to check broken external links in the Documentation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Documentation shouldn't have broken links. sphinx linkcheck builder scans all documents for external links, tries to open them with urllib2, and writes an overview which ones are broken and redirected to standard output and to output.txt in the output directory. Reviewed-by: Jani Nikula Tested-by: Jani Nikula Signed-off-by: Rémy Léone Signed-off-by: Jonathan Corbet --- Documentation/DocBook/Makefile | 1 + Documentation/Makefile.sphinx | 4 ++++ Documentation/media/Makefile | 1 + Makefile | 2 +- 4 files changed, 7 insertions(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 327bf57f4599..7b8831fb4e37 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -71,6 +71,7 @@ installmandocs: mandocs # no-op for the DocBook toolchain epubdocs: latexdocs: +linkcheckdocs: ### #External programs used diff --git a/Documentation/Makefile.sphinx b/Documentation/Makefile.sphinx index 8284f3d1b022..bcf529f6cf9b 100644 --- a/Documentation/Makefile.sphinx +++ b/Documentation/Makefile.sphinx @@ -69,6 +69,9 @@ quiet_cmd_sphinx = SPHINX $@ --> file://$(abspath $(BUILDDIR)/$3/$4) htmldocs: @+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,html,$(var),,$(var))) +linkcheckdocs: + @$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,linkcheck,$(var),,$(var))) + latexdocs: @+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,latex,$(var),latex,$(var))) @@ -117,6 +120,7 @@ dochelp: @echo ' pdfdocs - PDF' @echo ' epubdocs - EPUB' @echo ' xmldocs - XML' + @echo ' linkcheckdocs - check for broken external links (will connect to external hosts)' @echo ' cleandocs - clean all generated files' @echo @echo ' make SPHINXDIRS="s1 s2" [target] Generate only docs of folder s1, s2' diff --git a/Documentation/media/Makefile b/Documentation/media/Makefile index 730d73db7c7a..9b3e70b2cab2 100644 --- a/Documentation/media/Makefile +++ b/Documentation/media/Makefile @@ -103,6 +103,7 @@ html: all epub: all xml: all latex: $(IMGPDF) all +linkcheck: clean: -rm -f $(DOTTGT) $(IMGTGT) ${TARGETS} 2>/dev/null diff --git a/Makefile b/Makefile index ec411ba9e40f..96e29f9a9df8 100644 --- a/Makefile +++ b/Makefile @@ -1444,7 +1444,7 @@ $(help-board-dirs): help-%: # Documentation targets # --------------------------------------------------------------------------- -DOC_TARGETS := xmldocs sgmldocs psdocs latexdocs pdfdocs htmldocs mandocs installmandocs epubdocs cleandocs +DOC_TARGETS := xmldocs sgmldocs psdocs latexdocs pdfdocs htmldocs mandocs installmandocs epubdocs cleandocs linkcheckdocs PHONY += $(DOC_TARGETS) $(DOC_TARGETS): scripts_basic FORCE $(Q)$(MAKE) $(build)=scripts build_docproc build_check-lc_ctype -- cgit v1.2.3 From e3941cd9f59d1d5508c29eb1712a732722885ee7 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Mon, 20 Feb 2017 15:26:21 +0100 Subject: PM / docs: Fix structure references in device.rst There is a better way to represent structure references than it was done in device.rst by commit 730c4c053012 (PM / sleep / docs: Convert PM notifiers document to reST), which is to use "struct name" as a link caption (e.g. :c:type:`struct device `). That will cause sphinx to generate a proper reference to the data type in question (struct device in the example above) and "struct name" will work as the link in the HTML output. Fix device.rst by using that convention where applicable. Fixes: 730c4c053012 (PM / sleep / docs: Convert PM notifiers document to reST) Signed-off-by: Rafael J. Wysocki Signed-off-by: Jonathan Corbet --- Documentation/driver-api/pm/devices.rst | 72 +++++++++++++++++---------------- 1 file changed, 38 insertions(+), 34 deletions(-) (limited to 'Documentation') diff --git a/Documentation/driver-api/pm/devices.rst b/Documentation/driver-api/pm/devices.rst index 0e8cf4efd7e7..bedd32388dac 100644 --- a/Documentation/driver-api/pm/devices.rst +++ b/Documentation/driver-api/pm/devices.rst @@ -1,4 +1,10 @@ -.. |struct| replace:: :c:type:`struct` +.. |struct dev_pm_ops| replace:: :c:type:`struct dev_pm_ops ` +.. |struct dev_pm_domain| replace:: :c:type:`struct dev_pm_domain ` +.. |struct bus_type| replace:: :c:type:`struct bus_type ` +.. |struct device_type| replace:: :c:type:`struct device_type ` +.. |struct class| replace:: :c:type:`struct class ` +.. |struct wakeup_source| replace:: :c:type:`struct wakeup_source ` +.. |struct device| replace:: :c:type:`struct device ` ============================== Device Power Management Basics @@ -95,17 +101,17 @@ Device Power Management Operations Device power management operations, at the subsystem level as well as at the device driver level, are implemented by defining and populating objects of type -|struct| :c:type:`dev_pm_ops` defined in :file:`include/linux/pm.h`. -The roles of the methods included in it will be explained in what follows. For -now, it should be sufficient to remember that the last three methods are -specific to runtime power management while the remaining ones are used during -system-wide power transitions. +|struct dev_pm_ops| defined in :file:`include/linux/pm.h`. The roles of the +methods included in it will be explained in what follows. For now, it should be +sufficient to remember that the last three methods are specific to runtime power +management while the remaining ones are used during system-wide power +transitions. There also is a deprecated "old" or "legacy" interface for power management operations available at least for some subsystems. This approach does not use -|struct| :c:type:`dev_pm_ops` objects and it is suitable only for implementing -system sleep power management methods in a limited way. Therefore it is not -described in this document, so please refer directly to the source code for more +|struct dev_pm_ops| objects and it is suitable only for implementing system +sleep power management methods in a limited way. Therefore it is not described +in this document, so please refer directly to the source code for more information about it. @@ -113,14 +119,13 @@ Subsystem-Level Methods ----------------------- The core methods to suspend and resume devices reside in -|struct| :c:type:`dev_pm_ops` pointed to by the :c:member:`ops` -member of |struct| :c:type:`dev_pm_domain`, or by the :c:member:`pm` -member of |struct| :c:type:`bus_type`, |struct| :c:type:`device_type` and -|struct| :c:type:`class`. They are mostly of interest to the people writing -infrastructure for platforms and buses, like PCI or USB, or device type and -device class drivers. They also are relevant to the writers of device drivers -whose subsystems (PM domains, device types, device classes and bus types) don't -provide all power management methods. +|struct dev_pm_ops| pointed to by the :c:member:`ops` member of +|struct dev_pm_domain|, or by the :c:member:`pm` member of |struct bus_type|, +|struct device_type| and |struct class|. They are mostly of interest to the +people writing infrastructure for platforms and buses, like PCI or USB, or +device type and device class drivers. They also are relevant to the writers of +device drivers whose subsystems (PM domains, device types, device classes and +bus types) don't provide all power management methods. Bus drivers implement these methods as appropriate for the hardware and the drivers using it; PCI works differently from USB, and so on. Not many people @@ -145,12 +150,11 @@ The :c:member:`power.can_wakeup` flag just records whether the device (and its driver) can physically support wakeup events. The :c:func:`device_set_wakeup_capable()` routine affects this flag. The :c:member:`power.wakeup` field is a pointer to an object of type -|struct| :c:type:`wakeup_source` used for controlling whether or not -the device should use its system wakeup mechanism and for notifying the -PM core of system wakeup events signaled by the device. This object is only -present for wakeup-capable devices (i.e. devices whose -:c:member:`can_wakeup` flags are set) and is created (or removed) by -:c:func:`device_set_wakeup_capable()`. +|struct wakeup_source| used for controlling whether or not the device should use +its system wakeup mechanism and for notifying the PM core of system wakeup +events signaled by the device. This object is only present for wakeup-capable +devices (i.e. devices whose :c:member:`can_wakeup` flags are set) and is created +(or removed) by :c:func:`device_set_wakeup_capable()`. Whether or not a device is capable of issuing wakeup events is a hardware matter, and the kernel is responsible for keeping track of it. By contrast, @@ -670,17 +674,17 @@ nested inside another power domain. The nested domain is referred to as the sub-domain of the parent domain. Support for power domains is provided through the :c:member:`pm_domain` field of -|struct| :c:type:`device`. This field is a pointer to an object of -type |struct| :c:type:`dev_pm_domain`, defined in :file:`include/linux/pm.h``, -providing a set of power management callbacks analogous to the subsystem-level -and device driver callbacks that are executed for the given device during all -power transitions, instead of the respective subsystem-level callbacks. -Specifically, if a device's :c:member:`pm_domain` pointer is not NULL, the -``->suspend()`` callback from the object pointed to by it will be executed -instead of its subsystem's (e.g. bus type's) ``->suspend()`` callback and -analogously for all of the remaining callbacks. In other words, power -management domain callbacks, if defined for the given device, always take -precedence over the callbacks provided by the device's subsystem (e.g. bus type). +|struct device|. This field is a pointer to an object of type +|struct dev_pm_domain|, defined in :file:`include/linux/pm.h``, providing a set +of power management callbacks analogous to the subsystem-level and device driver +callbacks that are executed for the given device during all power transitions, +instead of the respective subsystem-level callbacks. Specifically, if a +device's :c:member:`pm_domain` pointer is not NULL, the ``->suspend()`` callback +from the object pointed to by it will be executed instead of its subsystem's +(e.g. bus type's) ``->suspend()`` callback and analogously for all of the +remaining callbacks. In other words, power management domain callbacks, if +defined for the given device, always take precedence over the callbacks provided +by the device's subsystem (e.g. bus type). The support for device power management domains is only relevant to platforms needing to use the same device driver power management callbacks in many -- cgit v1.2.3 From bd8562626c8e170691d6457fe4e8dfb45607a48d Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Mon, 20 Feb 2017 15:28:13 +0100 Subject: docs / driver-api: Fix structure references in device_link.rst The format of the structure references in device_link.rst is incorrect, because it doesn't cause proper references to the struct data types to be generated (for struct dev_pm_domain in particular). Fix that by using the :c:type:`struct name ` convention for encoding references to struct data types. Fixes: aad800403a87 (Documentation/core-api/device_link: Add initial documentation) Signed-off-by: Rafael J. Wysocki Signed-off-by: Jonathan Corbet --- Documentation/driver-api/device_link.rst | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) (limited to 'Documentation') diff --git a/Documentation/driver-api/device_link.rst b/Documentation/driver-api/device_link.rst index 5f5713448703..70e328e16aad 100644 --- a/Documentation/driver-api/device_link.rst +++ b/Documentation/driver-api/device_link.rst @@ -1,3 +1,6 @@ +.. |struct dev_pm_domain| replace:: :c:type:`struct dev_pm_domain ` +.. |struct generic_pm_domain| replace:: :c:type:`struct generic_pm_domain ` + ============ Device links ============ @@ -120,12 +123,11 @@ Examples is the same as if the MMU was the parent of the master device. The fact that both devices share the same power domain would normally - suggest usage of a :c:type:`struct dev_pm_domain` or :c:type:`struct - generic_pm_domain`, however these are not independent devices that - happen to share a power switch, but rather the MMU device serves the - busmaster device and is useless without it. A device link creates a - synthetic hierarchical relationship between the devices and is thus - more apt. + suggest usage of a |struct dev_pm_domain| or |struct generic_pm_domain|, + however these are not independent devices that happen to share a power + switch, but rather the MMU device serves the busmaster device and is + useless without it. A device link creates a synthetic hierarchical + relationship between the devices and is thus more apt. * A Thunderbolt host controller comprises a number of PCIe hotplug ports and an NHI device to manage the PCIe switch. On resume from system sleep, @@ -157,7 +159,7 @@ Examples Alternatives ============ -* A :c:type:`struct dev_pm_domain` can be used to override the bus, +* A |struct dev_pm_domain| can be used to override the bus, class or device type callbacks. It is intended for devices sharing a single on/off switch, however it does not guarantee a specific suspend/resume ordering, this needs to be implemented separately. @@ -166,7 +168,7 @@ Alternatives suspended. Furthermore it cannot be used to enforce a specific shutdown ordering or a driver presence dependency. -* A :c:type:`struct generic_pm_domain` is a lot more heavyweight than a +* A |struct generic_pm_domain| is a lot more heavyweight than a device link and does not allow for shutdown ordering or driver presence dependencies. It also cannot be used on ACPI systems. -- cgit v1.2.3