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