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diff --git a/Documentation/hwmon/hwmon-kernel-api.rst b/Documentation/hwmon/hwmon-kernel-api.rst new file mode 100644 index 000000000000..c41eb6108103 --- /dev/null +++ b/Documentation/hwmon/hwmon-kernel-api.rst @@ -0,0 +1,386 @@ +The Linux Hardware Monitoring kernel API +======================================== + +Guenter Roeck + +Introduction +------------ + +This document describes the API that can be used by hardware monitoring +drivers that want to use the hardware monitoring framework. + +This document does not describe what a hardware monitoring (hwmon) Driver or +Device is. It also does not describe the API which can be used by user space +to communicate with a hardware monitoring device. If you want to know this +then please read the following file: Documentation/hwmon/sysfs-interface.rst. + +For additional guidelines on how to write and improve hwmon drivers, please +also read Documentation/hwmon/submitting-patches.rst. + +The API +------- +Each hardware monitoring driver must #include <linux/hwmon.h> and, in most +cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following +register/unregister functions:: + + struct device * + hwmon_device_register_with_groups(struct device *dev, const char *name, + void *drvdata, + const struct attribute_group **groups); + + struct device * + devm_hwmon_device_register_with_groups(struct device *dev, + const char *name, void *drvdata, + const struct attribute_group **groups); + + struct device * + hwmon_device_register_with_info(struct device *dev, + const char *name, void *drvdata, + const struct hwmon_chip_info *info, + const struct attribute_group **extra_groups); + + struct device * + devm_hwmon_device_register_with_info(struct device *dev, + const char *name, + void *drvdata, + const struct hwmon_chip_info *info, + const struct attribute_group **extra_groups); + + void hwmon_device_unregister(struct device *dev); + + void devm_hwmon_device_unregister(struct device *dev); + +hwmon_device_register_with_groups registers a hardware monitoring device. +The first parameter of this function is a pointer to the parent device. +The name parameter is a pointer to the hwmon device name. The registration +function wil create a name sysfs attribute pointing to this name. +The drvdata parameter is the pointer to the local driver data. +hwmon_device_register_with_groups will attach this pointer to the newly +allocated hwmon device. The pointer can be retrieved by the driver using +dev_get_drvdata() on the hwmon device pointer. The groups parameter is +a pointer to a list of sysfs attribute groups. The list must be NULL terminated. +hwmon_device_register_with_groups creates the hwmon device with name attribute +as well as all sysfs attributes attached to the hwmon device. +This function returns a pointer to the newly created hardware monitoring device +or PTR_ERR for failure. + +devm_hwmon_device_register_with_groups is similar to +hwmon_device_register_with_groups. However, it is device managed, meaning the +hwmon device does not have to be removed explicitly by the removal function. + +hwmon_device_register_with_info is the most comprehensive and preferred means +to register a hardware monitoring device. It creates the standard sysfs +attributes in the hardware monitoring core, letting the driver focus on reading +from and writing to the chip instead of having to bother with sysfs attributes. +The parent device parameter cannot be NULL with non-NULL chip info. Its +parameters are described in more detail below. + +devm_hwmon_device_register_with_info is similar to +hwmon_device_register_with_info. However, it is device managed, meaning the +hwmon device does not have to be removed explicitly by the removal function. + +hwmon_device_unregister deregisters a registered hardware monitoring device. +The parameter of this function is the pointer to the registered hardware +monitoring device structure. This function must be called from the driver +remove function if the hardware monitoring device was registered with +hwmon_device_register_with_groups or hwmon_device_register_with_info. + +devm_hwmon_device_unregister does not normally have to be called. It is only +needed for error handling, and only needed if the driver probe fails after +the call to devm_hwmon_device_register_with_groups or +hwmon_device_register_with_info and if the automatic (device managed) +removal would be too late. + +All supported hwmon device registration functions only accept valid device +names. Device names including invalid characters (whitespace, '*', or '-') +will be rejected. The 'name' parameter is mandatory. + +Using devm_hwmon_device_register_with_info() +-------------------------------------------- + +hwmon_device_register_with_info() registers a hardware monitoring device. +The parameters to this function are + +=============================================== =============================================== +`struct device *dev` Pointer to parent device +`const char *name` Device name +`void *drvdata` Driver private data +`const struct hwmon_chip_info *info` Pointer to chip description. +`const struct attribute_group **extra_groups` Null-terminated list of additional non-standard + sysfs attribute groups. +=============================================== =============================================== + +This function returns a pointer to the created hardware monitoring device +on success and a negative error code for failure. + +The hwmon_chip_info structure looks as follows:: + + struct hwmon_chip_info { + const struct hwmon_ops *ops; + const struct hwmon_channel_info **info; + }; + +It contains the following fields: + +* ops: + Pointer to device operations. +* info: + NULL-terminated list of device channel descriptors. + +The list of hwmon operations is defined as:: + + struct hwmon_ops { + umode_t (*is_visible)(const void *, enum hwmon_sensor_types type, + u32 attr, int); + int (*read)(struct device *, enum hwmon_sensor_types type, + u32 attr, int, long *); + int (*write)(struct device *, enum hwmon_sensor_types type, + u32 attr, int, long); + }; + +It defines the following operations. + +* is_visible: + Pointer to a function to return the file mode for each supported + attribute. This function is mandatory. + +* read: + Pointer to a function for reading a value from the chip. This function + is optional, but must be provided if any readable attributes exist. + +* write: + Pointer to a function for writing a value to the chip. This function is + optional, but must be provided if any writeable attributes exist. + +Each sensor channel is described with struct hwmon_channel_info, which is +defined as follows:: + + struct hwmon_channel_info { + enum hwmon_sensor_types type; + u32 *config; + }; + +It contains following fields: + +* type: + The hardware monitoring sensor type. + + Supported sensor types are + + ================== ================================================== + hwmon_chip A virtual sensor type, used to describe attributes + which are not bound to a specific input or output + hwmon_temp Temperature sensor + hwmon_in Voltage sensor + hwmon_curr Current sensor + hwmon_power Power sensor + hwmon_energy Energy sensor + hwmon_humidity Humidity sensor + hwmon_fan Fan speed sensor + hwmon_pwm PWM control + ================== ================================================== + +* config: + Pointer to a 0-terminated list of configuration values for each + sensor of the given type. Each value is a combination of bit values + describing the attributes supposed by a single sensor. + +As an example, here is the complete description file for a LM75 compatible +sensor chip. The chip has a single temperature sensor. The driver wants to +register with the thermal subsystem (HWMON_C_REGISTER_TZ), and it supports +the update_interval attribute (HWMON_C_UPDATE_INTERVAL). The chip supports +reading the temperature (HWMON_T_INPUT), it has a maximum temperature +register (HWMON_T_MAX) as well as a maximum temperature hysteresis register +(HWMON_T_MAX_HYST):: + + static const u32 lm75_chip_config[] = { + HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL, + 0 + }; + + static const struct hwmon_channel_info lm75_chip = { + .type = hwmon_chip, + .config = lm75_chip_config, + }; + + static const u32 lm75_temp_config[] = { + HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST, + 0 + }; + + static const struct hwmon_channel_info lm75_temp = { + .type = hwmon_temp, + .config = lm75_temp_config, + }; + + static const struct hwmon_channel_info *lm75_info[] = { + &lm75_chip, + &lm75_temp, + NULL + }; + + The HWMON_CHANNEL_INFO() macro can and should be used when possible. + With this macro, the above example can be simplified to + + static const struct hwmon_channel_info *lm75_info[] = { + HWMON_CHANNEL_INFO(chip, + HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL), + HWMON_CHANNEL_INFO(temp, + HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST), + NULL + }; + + The remaining declarations are as follows. + + static const struct hwmon_ops lm75_hwmon_ops = { + .is_visible = lm75_is_visible, + .read = lm75_read, + .write = lm75_write, + }; + + static const struct hwmon_chip_info lm75_chip_info = { + .ops = &lm75_hwmon_ops, + .info = lm75_info, + }; + +A complete list of bit values indicating individual attribute support +is defined in include/linux/hwmon.h. Definition prefixes are as follows. + +=============== ================================================= +HWMON_C_xxxx Chip attributes, for use with hwmon_chip. +HWMON_T_xxxx Temperature attributes, for use with hwmon_temp. +HWMON_I_xxxx Voltage attributes, for use with hwmon_in. +HWMON_C_xxxx Current attributes, for use with hwmon_curr. + Notice the prefix overlap with chip attributes. +HWMON_P_xxxx Power attributes, for use with hwmon_power. +HWMON_E_xxxx Energy attributes, for use with hwmon_energy. +HWMON_H_xxxx Humidity attributes, for use with hwmon_humidity. +HWMON_F_xxxx Fan speed attributes, for use with hwmon_fan. +HWMON_PWM_xxxx PWM control attributes, for use with hwmon_pwm. +=============== ================================================= + +Driver callback functions +------------------------- + +Each driver provides is_visible, read, and write functions. Parameters +and return values for those functions are as follows:: + + umode_t is_visible_func(const void *data, enum hwmon_sensor_types type, + u32 attr, int channel) + +Parameters: + data: + Pointer to device private data structure. + type: + The sensor type. + attr: + Attribute identifier associated with a specific attribute. + For example, the attribute value for HWMON_T_INPUT would be + hwmon_temp_input. For complete mappings of bit fields to + attribute values please see include/linux/hwmon.h. + channel: + The sensor channel number. + +Return value: + The file mode for this attribute. Typically, this will be 0 (the + attribute will not be created), S_IRUGO, or 'S_IRUGO | S_IWUSR'. + +:: + + int read_func(struct device *dev, enum hwmon_sensor_types type, + u32 attr, int channel, long *val) + +Parameters: + dev: + Pointer to the hardware monitoring device. + type: + The sensor type. + attr: + Attribute identifier associated with a specific attribute. + For example, the attribute value for HWMON_T_INPUT would be + hwmon_temp_input. For complete mappings please see + include/linux/hwmon.h. + channel: + The sensor channel number. + val: + Pointer to attribute value. + +Return value: + 0 on success, a negative error number otherwise. + +:: + + int write_func(struct device *dev, enum hwmon_sensor_types type, + u32 attr, int channel, long val) + +Parameters: + dev: + Pointer to the hardware monitoring device. + type: + The sensor type. + attr: + Attribute identifier associated with a specific attribute. + For example, the attribute value for HWMON_T_INPUT would be + hwmon_temp_input. For complete mappings please see + include/linux/hwmon.h. + channel: + The sensor channel number. + val: + The value to write to the chip. + +Return value: + 0 on success, a negative error number otherwise. + + +Driver-provided sysfs attributes +-------------------------------- + +If the hardware monitoring device is registered with +hwmon_device_register_with_info or devm_hwmon_device_register_with_info, +it is most likely not necessary to provide sysfs attributes. Only additional +non-standard sysfs attributes need to be provided when one of those registration +functions is used. + +The header file linux/hwmon-sysfs.h provides a number of useful macros to +declare and use hardware monitoring sysfs attributes. + +In many cases, you can use the exsting define DEVICE_ATTR or its variants +DEVICE_ATTR_{RW,RO,WO} to declare such attributes. This is feasible if an +attribute has no additional context. However, in many cases there will be +additional information such as a sensor index which will need to be passed +to the sysfs attribute handling function. + +SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes +which need such additional context information. SENSOR_DEVICE_ATTR requires +one additional argument, SENSOR_DEVICE_ATTR_2 requires two. + +Simplified variants of SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 are available +and should be used if standard attribute permissions and function names are +feasible. Standard permissions are 0644 for SENSOR_DEVICE_ATTR[_2]_RW, +0444 for SENSOR_DEVICE_ATTR[_2]_RO, and 0200 for SENSOR_DEVICE_ATTR[_2]_WO. +Standard functions, similar to DEVICE_ATTR_{RW,RO,WO}, have _show and _store +appended to the provided function name. + +SENSOR_DEVICE_ATTR and its variants define a struct sensor_device_attribute +variable. This structure has the following fields:: + + struct sensor_device_attribute { + struct device_attribute dev_attr; + int index; + }; + +You can use to_sensor_dev_attr to get the pointer to this structure from the +attribute read or write function. Its parameter is the device to which the +attribute is attached. + +SENSOR_DEVICE_ATTR_2 and its variants define a struct sensor_device_attribute_2 +variable, which is defined as follows:: + + struct sensor_device_attribute_2 { + struct device_attribute dev_attr; + u8 index; + u8 nr; + }; + +Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter +is the device to which the attribute is attached. |