From 3f19fed8d0daed6e0e04b130d203d4333b757901 Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Fri, 26 Nov 2021 09:16:11 +0100 Subject: Documentation: add TTY chapter We now have all the kernel-doc comments in the code ready. So add a couple of documents dragging those into generated docs from Documentation/. There is only some sugar text around included kernel-docs here. It's a complete chapter, to be extended later as desired. This is a solid cornerstone for the time being, I believe. Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20211126081611.11001-24-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman --- Documentation/index.rst | 1 + Documentation/tty/index.rst | 63 ++++++++++++++++++ Documentation/tty/n_tty.rst | 22 +++++++ Documentation/tty/tty_buffer.rst | 46 +++++++++++++ Documentation/tty/tty_driver.rst | 128 ++++++++++++++++++++++++++++++++++++ Documentation/tty/tty_internals.rst | 31 +++++++++ Documentation/tty/tty_ldisc.rst | 6 ++ Documentation/tty/tty_port.rst | 70 ++++++++++++++++++++ Documentation/tty/tty_struct.rst | 81 +++++++++++++++++++++++ 9 files changed, 448 insertions(+) create mode 100644 Documentation/tty/index.rst create mode 100644 Documentation/tty/n_tty.rst create mode 100644 Documentation/tty/tty_buffer.rst create mode 100644 Documentation/tty/tty_driver.rst create mode 100644 Documentation/tty/tty_internals.rst create mode 100644 Documentation/tty/tty_port.rst create mode 100644 Documentation/tty/tty_struct.rst (limited to 'Documentation') diff --git a/Documentation/index.rst b/Documentation/index.rst index 54ce34fd6fbd..2b4de3926858 100644 --- a/Documentation/index.rst +++ b/Documentation/index.rst @@ -137,6 +137,7 @@ needed). misc-devices/index scheduler/index mhi/index + tty/index Architecture-agnostic documentation ----------------------------------- diff --git a/Documentation/tty/index.rst b/Documentation/tty/index.rst new file mode 100644 index 000000000000..21ea0cb21e55 --- /dev/null +++ b/Documentation/tty/index.rst @@ -0,0 +1,63 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=== +TTY +=== + +Teletypewriter (TTY) layer takes care of all those serial devices. Including +the virtual ones like pseudoterminal (PTY). + +TTY structures +============== + +There are several major TTY structures. Every TTY device in a system has a +corresponding struct tty_port. These devices are maintained by a TTY driver +which is struct tty_driver. This structure describes the driver but also +contains a reference to operations which could be performed on the TTYs. It is +struct tty_operations. Then, upon open, a struct tty_struct is allocated and +lives until the final close. During this time, several callbacks from struct +tty_operations are invoked by the TTY layer. + +Every character received by the kernel (both from devices and users) is passed +through a preselected :doc:`tty_ldisc` (in +short ldisc; in C, struct tty_ldisc_ops). Its task is to transform characters +as defined by a particular ldisc or by user too. The default one is n_tty, +implementing echoes, signal handling, jobs control, special characters +processing, and more. The transformed characters are passed further to +user/device, depending on the source. + +In-detail description of the named TTY structures is in separate documents: + +.. toctree:: + :maxdepth: 2 + + tty_driver + tty_port + tty_struct + tty_ldisc + tty_buffer + n_tty + tty_internals + +Writing TTY Driver +================== + +Before one starts writing a TTY driver, they must consider +:doc:`Serial <../driver-api/serial/driver>` and :doc:`USB Serial +<../usb/usb-serial>` layers +first. Drivers for serial devices can often use one of these specific layers to +implement a serial driver. Only special devices should be handled directly by +the TTY Layer. If you are about to write such a driver, read on. + +A *typical* sequence a TTY driver performs is as follows: + +#. Allocate and register a TTY driver (module init) +#. Create and register TTY devices as they are probed (probe function) +#. Handle TTY operations and events like interrupts (TTY core invokes the + former, the device the latter) +#. Remove devices as they are going away (remove function) +#. Unregister and free the TTY driver (module exit) + +Steps regarding driver, i.e. 1., 3., and 5. are described in detail in +:doc:`tty_driver`. For the other two (devices handling), look into +:doc:`tty_port`. diff --git a/Documentation/tty/n_tty.rst b/Documentation/tty/n_tty.rst new file mode 100644 index 000000000000..15b70faee72d --- /dev/null +++ b/Documentation/tty/n_tty.rst @@ -0,0 +1,22 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===== +N_TTY +===== + +.. contents:: :local: + +The default (and fallback) :doc:`TTY line discipline `. It tries to +handle characters as per POSIX. + +External Functions +================== + +.. kernel-doc:: drivers/tty/n_tty.c + :export: + +Internal Functions +================== + +.. kernel-doc:: drivers/tty/n_tty.c + :internal: diff --git a/Documentation/tty/tty_buffer.rst b/Documentation/tty/tty_buffer.rst new file mode 100644 index 000000000000..a39d4781e0d2 --- /dev/null +++ b/Documentation/tty/tty_buffer.rst @@ -0,0 +1,46 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========== +TTY Buffer +========== + +.. contents:: :local: + +Here, we document functions for taking care of tty buffer and their flipping. +Drivers are supposed to fill the buffer by one of those functions below and +then flip the buffer, so that the data are passed to :doc:`line discipline +` for further processing. + +Flip Buffer Management +====================== + +.. kernel-doc:: drivers/tty/tty_buffer.c + :identifiers: tty_prepare_flip_string tty_insert_flip_string_fixed_flag + tty_insert_flip_string_flags __tty_insert_flip_char + tty_flip_buffer_push tty_ldisc_receive_buf + +---- + +Other Functions +=============== + +.. kernel-doc:: drivers/tty/tty_buffer.c + :identifiers: tty_buffer_space_avail tty_buffer_set_limit + +---- + +Buffer Locking +============== + +These are used only in special circumstances. Avoid them. + +.. kernel-doc:: drivers/tty/tty_buffer.c + :identifiers: tty_buffer_lock_exclusive tty_buffer_unlock_exclusive + +---- + +Internal Functions +================== + +.. kernel-doc:: drivers/tty/tty_buffer.c + :internal: diff --git a/Documentation/tty/tty_driver.rst b/Documentation/tty/tty_driver.rst new file mode 100644 index 000000000000..cc529f863406 --- /dev/null +++ b/Documentation/tty/tty_driver.rst @@ -0,0 +1,128 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================= +TTY Driver and TTY Operations +============================= + +.. contents:: :local: + +Allocation +========== + +The first thing a driver needs to do is to allocate a struct tty_driver. This +is done by tty_alloc_driver() (or __tty_alloc_driver()). Next, the newly +allocated structure is filled with information. See `TTY Driver Reference`_ at +the end of this document on what actually shall be filled in. + +The allocation routines expect a number of devices the driver can handle at +most and flags. Flags are those starting ``TTY_DRIVER_`` listed and described +in `TTY Driver Flags`_ below. + +When the driver is about to be freed, tty_driver_kref_put() is called on that. +It will decrements the reference count and if it reaches zero, the driver is +freed. + +For reference, both allocation and deallocation functions are explained here in +detail: + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: __tty_alloc_driver tty_driver_kref_put + +TTY Driver Flags +---------------- + +Here comes the documentation of flags accepted by tty_alloc_driver() (or +__tty_alloc_driver()): + +.. kernel-doc:: include/linux/tty_driver.h + :doc: TTY Driver Flags + +---- + +Registration +============ + +When a struct tty_driver is allocated and filled in, it can be registered using +tty_register_driver(). It is recommended to pass ``TTY_DRIVER_DYNAMIC_DEV`` in +flags of tty_alloc_driver(). If it is not passed, *all* devices are also +registered during tty_register_driver() and the following paragraph of +registering devices can be skipped for such drivers. However, the struct +tty_port part in `Registering Devices`_ is still relevant there. + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_register_driver tty_unregister_driver + +Registering Devices +------------------- + +Every TTY device shall be backed by a struct tty_port. Usually, TTY drivers +embed tty_port into device's private structures. Further details about handling +tty_port can be found in :doc:`tty_port`. The driver is also recommended to use +tty_port's reference counting by tty_port_get() and tty_port_put(). The final +put is supposed to free the tty_port including the device's private struct. + +Unless ``TTY_DRIVER_DYNAMIC_DEV`` was passed as flags to tty_alloc_driver(), +TTY driver is supposed to register every device discovered in the system +(the latter is preferred). This is performed by tty_register_device(). Or by +tty_register_device_attr() if the driver wants to expose some information +through struct attribute_group. Both of them register ``index``'th device and +upon return, the device can be opened. There are also preferred tty_port +variants described in `Linking Devices to Ports`_ later. It is up to driver to +manage free indices and choosing the right one. The TTY layer only refuses to +register more devices than passed to tty_alloc_driver(). + +When the device is opened, the TTY layer allocates struct tty_struct and starts +calling operations from :c:member:`tty_driver.ops`, see `TTY Operations +Reference`_. + +The registration routines are documented as follows: + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_register_device tty_register_device_attr + tty_unregister_device + +---- + +Linking Devices to Ports +------------------------ +As stated earlier, every TTY device shall have a struct tty_port assigned to +it. It must be known to the TTY layer at :c:member:`tty_driver.ops.install()` +at latest. There are few helpers to *link* the two. Ideally, the driver uses +tty_port_register_device() or tty_port_register_device_attr() instead of +tty_register_device() and tty_register_device_attr() at the registration time. +This way, the driver needs not care about linking later on. + +If that is not possible, the driver still can link the tty_port to a specific +index *before* the actual registration by tty_port_link_device(). If it still +does not fit, tty_port_install() can be used from the +:c:member:`tty_driver.ops.install` hook as a last resort. The last one is +dedicated mostly for in-memory devices like PTY where tty_ports are allocated +on demand. + +The linking routines are documented here: + +.. kernel-doc:: drivers/tty/tty_port.c + :identifiers: tty_port_link_device tty_port_register_device + tty_port_register_device_attr + +---- + +TTY Driver Reference +==================== + +All members of struct tty_driver are documented here. The required members are +noted at the end. struct tty_operations are documented next. + +.. kernel-doc:: include/linux/tty_driver.h + :identifiers: tty_driver + +---- + +TTY Operations Reference +======================== + +When a TTY is registered, these driver hooks can be invoked by the TTY layer: + +.. kernel-doc:: include/linux/tty_driver.h + :identifiers: tty_operations + diff --git a/Documentation/tty/tty_internals.rst b/Documentation/tty/tty_internals.rst new file mode 100644 index 000000000000..d0d415820300 --- /dev/null +++ b/Documentation/tty/tty_internals.rst @@ -0,0 +1,31 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +TTY Internals +============= + +.. contents:: :local: + +Kopen +===== + +These functions serve for opening a TTY from the kernelspace: + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_kopen_exclusive tty_kopen_shared tty_kclose + +---- + +Exported Internal Functions +=========================== + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_release_struct tty_dev_name_to_number tty_get_icount + +---- + +Internal Functions +================== + +.. kernel-doc:: drivers/tty/tty_io.c + :internal: diff --git a/Documentation/tty/tty_ldisc.rst b/Documentation/tty/tty_ldisc.rst index 65885d97595c..5144751be804 100644 --- a/Documentation/tty/tty_ldisc.rst +++ b/Documentation/tty/tty_ldisc.rst @@ -6,6 +6,12 @@ TTY Line Discipline .. contents:: :local: +TTY line discipline process all incoming and outgoing character from/to a tty +device. The default line discipline is :doc:`N_TTY `. It is also a +fallback if establishing any other discipline for a tty fails. If even N_TTY +fails, N_NULL takes over. That never fails, but also does not process any +characters -- it throws them away. + Registration ============ diff --git a/Documentation/tty/tty_port.rst b/Documentation/tty/tty_port.rst new file mode 100644 index 000000000000..5cb90e954fcf --- /dev/null +++ b/Documentation/tty/tty_port.rst @@ -0,0 +1,70 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======== +TTY Port +======== + +.. contents:: :local: + +The TTY drivers are advised to use struct tty_port helpers as much as possible. +If the drivers implement :c:member:`tty_port.ops.activate()` and +:c:member:`tty_port.ops.shutdown()`, they can use tty_port_open(), +tty_port_close(), and tty_port_hangup() in respective +:c:member:`tty_struct.ops` hooks. + +The reference and details are contained in the `TTY Port Reference`_ and `TTY +Port Operations Reference`_ sections at the bottom. + +TTY Port Functions +================== + +Init & Destroy +-------------- + +.. kernel-doc:: drivers/tty/tty_port.c + :identifiers: tty_port_init tty_port_destroy + tty_port_get tty_port_put + +Open/Close/Hangup Helpers +------------------------- + +.. kernel-doc:: drivers/tty/tty_port.c + :identifiers: tty_port_install tty_port_open tty_port_block_til_ready + tty_port_close tty_port_close_start tty_port_close_end tty_port_hangup + tty_port_shutdown + +TTY Refcounting +--------------- + +.. kernel-doc:: drivers/tty/tty_port.c + :identifiers: tty_port_tty_get tty_port_tty_set + +TTY Helpers +----------- + +.. kernel-doc:: drivers/tty/tty_port.c + :identifiers: tty_port_tty_hangup tty_port_tty_wakeup + + +Modem Signals +------------- + +.. kernel-doc:: drivers/tty/tty_port.c + :identifiers: tty_port_carrier_raised tty_port_raise_dtr_rts + tty_port_lower_dtr_rts + +---- + +TTY Port Reference +================== + +.. kernel-doc:: include/linux/tty_port.h + :identifiers: tty_port + +---- + +TTY Port Operations Reference +============================= + +.. kernel-doc:: include/linux/tty_port.h + :identifiers: tty_port_operations diff --git a/Documentation/tty/tty_struct.rst b/Documentation/tty/tty_struct.rst new file mode 100644 index 000000000000..c72f5a4293b2 --- /dev/null +++ b/Documentation/tty/tty_struct.rst @@ -0,0 +1,81 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========== +TTY Struct +========== + +.. contents:: :local: + +struct tty_struct is allocated by the TTY layer upon the first open of the TTY +device and released after the last close. The TTY layer passes this structure +to most of struct tty_operation's hooks. Members of tty_struct are documented +in `TTY Struct Reference`_ at the bottom. + +Initialization +============== + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_init_termios + +Name +==== + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_name + +Reference counting +================== + +.. kernel-doc:: include/linux/tty.h + :identifiers: tty_kref_get + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_kref_put + +Install +======= + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_standard_install + +Read & Write +============ + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_put_char + +Start & Stop +============ + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: start_tty stop_tty + +Wakeup +====== + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_wakeup + +Hangup +====== + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_hangup tty_vhangup tty_hung_up_p + +Misc +==== + +.. kernel-doc:: drivers/tty/tty_io.c + :identifiers: tty_do_resize + +TTY Struct Flags +================ + +.. kernel-doc:: include/linux/tty.h + :doc: TTY Struct Flags + +TTY Struct Reference +==================== + +.. kernel-doc:: include/linux/tty.h + :identifiers: tty_struct -- cgit v1.2.3