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diff --git a/Documentation/hwmon/hwmon-kernel-api.txt b/Documentation/hwmon/hwmon-kernel-api.txt new file mode 100644 index 00000000000..2ecdbfc85ec --- /dev/null +++ b/Documentation/hwmon/hwmon-kernel-api.txt @@ -0,0 +1,107 @@ +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. + +For additional guidelines on how to write and improve hwmon drivers, please +also read Documentation/hwmon/submitting-patches. + +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(struct device *dev); +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); + +void hwmon_device_unregister(struct device *dev); +void devm_hwmon_device_unregister(struct device *dev); + +hwmon_device_register registers a hardware monitoring device. The parameter +of this function is a pointer to the parent device. +This function returns a pointer to the newly created hardware monitoring device +or PTR_ERR for failure. If this registration function is used, hardware +monitoring sysfs attributes are expected to have been created and attached to +the parent device prior to calling hwmon_device_register. A name attribute must +have been created by the caller. + +hwmon_device_register_with_groups is similar to hwmon_device_register. However, +it has additional parameters. 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. + +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_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 or with hwmon_device_register_with_groups. + +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. + +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 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. + +SENSOR_DEVICE_ATTR defines 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 defines 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. |