1 The Linux Hardware Monitoring kernel API
2 ========================================
9 This document describes the API that can be used by hardware monitoring
10 drivers that want to use the hardware monitoring framework.
12 This document does not describe what a hardware monitoring (hwmon) Driver or
13 Device is. It also does not describe the API which can be used by user space
14 to communicate with a hardware monitoring device. If you want to know this
15 then please read the following file: Documentation/hwmon/sysfs-interface.rst.
17 For additional guidelines on how to write and improve hwmon drivers, please
18 also read Documentation/hwmon/submitting-patches.rst.
22 Each hardware monitoring driver must #include <linux/hwmon.h> and, in most
23 cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following
24 register/unregister functions::
27 hwmon_device_register_with_groups(struct device *dev, const char *name,
29 const struct attribute_group **groups);
32 devm_hwmon_device_register_with_groups(struct device *dev,
33 const char *name, void *drvdata,
34 const struct attribute_group **groups);
37 hwmon_device_register_with_info(struct device *dev,
38 const char *name, void *drvdata,
39 const struct hwmon_chip_info *info,
40 const struct attribute_group **extra_groups);
43 devm_hwmon_device_register_with_info(struct device *dev,
46 const struct hwmon_chip_info *info,
47 const struct attribute_group **extra_groups);
49 void hwmon_device_unregister(struct device *dev);
51 void devm_hwmon_device_unregister(struct device *dev);
53 char *hwmon_sanitize_name(const char *name);
55 char *devm_hwmon_sanitize_name(struct device *dev, const char *name);
57 hwmon_device_register_with_groups registers a hardware monitoring device.
58 The first parameter of this function is a pointer to the parent device.
59 The name parameter is a pointer to the hwmon device name. The registration
60 function wil create a name sysfs attribute pointing to this name.
61 The drvdata parameter is the pointer to the local driver data.
62 hwmon_device_register_with_groups will attach this pointer to the newly
63 allocated hwmon device. The pointer can be retrieved by the driver using
64 dev_get_drvdata() on the hwmon device pointer. The groups parameter is
65 a pointer to a list of sysfs attribute groups. The list must be NULL terminated.
66 hwmon_device_register_with_groups creates the hwmon device with name attribute
67 as well as all sysfs attributes attached to the hwmon device.
68 This function returns a pointer to the newly created hardware monitoring device
69 or PTR_ERR for failure.
71 devm_hwmon_device_register_with_groups is similar to
72 hwmon_device_register_with_groups. However, it is device managed, meaning the
73 hwmon device does not have to be removed explicitly by the removal function.
75 hwmon_device_register_with_info is the most comprehensive and preferred means
76 to register a hardware monitoring device. It creates the standard sysfs
77 attributes in the hardware monitoring core, letting the driver focus on reading
78 from and writing to the chip instead of having to bother with sysfs attributes.
79 The parent device parameter as well as the chip parameter must not be NULL. Its
80 parameters are described in more detail below.
82 devm_hwmon_device_register_with_info is similar to
83 hwmon_device_register_with_info. However, it is device managed, meaning the
84 hwmon device does not have to be removed explicitly by the removal function.
86 hwmon_device_unregister deregisters a registered hardware monitoring device.
87 The parameter of this function is the pointer to the registered hardware
88 monitoring device structure. This function must be called from the driver
89 remove function if the hardware monitoring device was registered with
90 hwmon_device_register_with_groups or hwmon_device_register_with_info.
92 devm_hwmon_device_unregister does not normally have to be called. It is only
93 needed for error handling, and only needed if the driver probe fails after
94 the call to devm_hwmon_device_register_with_groups or
95 hwmon_device_register_with_info and if the automatic (device managed)
96 removal would be too late.
98 All supported hwmon device registration functions only accept valid device
99 names. Device names including invalid characters (whitespace, '*', or '-')
100 will be rejected. The 'name' parameter is mandatory.
102 If the driver doesn't use a static device name (for example it uses
103 dev_name()), and therefore cannot make sure the name only contains valid
104 characters, hwmon_sanitize_name can be used. This convenience function
105 will duplicate the string and replace any invalid characters with an
106 underscore. It will allocate memory for the new string and it is the
107 responsibility of the caller to release the memory when the device is
110 devm_hwmon_sanitize_name is the resource managed version of
111 hwmon_sanitize_name; the memory will be freed automatically on device
114 Using devm_hwmon_device_register_with_info()
115 --------------------------------------------
117 hwmon_device_register_with_info() registers a hardware monitoring device.
118 The parameters to this function are
120 =============================================== ===============================================
121 `struct device *dev` Pointer to parent device
122 `const char *name` Device name
123 `void *drvdata` Driver private data
124 `const struct hwmon_chip_info *info` Pointer to chip description.
125 `const struct attribute_group **extra_groups` Null-terminated list of additional non-standard
126 sysfs attribute groups.
127 =============================================== ===============================================
129 This function returns a pointer to the created hardware monitoring device
130 on success and a negative error code for failure.
132 The hwmon_chip_info structure looks as follows::
134 struct hwmon_chip_info {
135 const struct hwmon_ops *ops;
136 const struct hwmon_channel_info **info;
139 It contains the following fields:
142 Pointer to device operations.
144 NULL-terminated list of device channel descriptors.
146 The list of hwmon operations is defined as::
149 umode_t (*is_visible)(const void *, enum hwmon_sensor_types type,
151 int (*read)(struct device *, enum hwmon_sensor_types type,
152 u32 attr, int, long *);
153 int (*write)(struct device *, enum hwmon_sensor_types type,
154 u32 attr, int, long);
157 It defines the following operations.
160 Pointer to a function to return the file mode for each supported
161 attribute. This function is mandatory.
164 Pointer to a function for reading a value from the chip. This function
165 is optional, but must be provided if any readable attributes exist.
168 Pointer to a function for writing a value to the chip. This function is
169 optional, but must be provided if any writeable attributes exist.
171 Each sensor channel is described with struct hwmon_channel_info, which is
174 struct hwmon_channel_info {
175 enum hwmon_sensor_types type;
179 It contains following fields:
182 The hardware monitoring sensor type.
184 Supported sensor types are
186 ================== ==================================================
187 hwmon_chip A virtual sensor type, used to describe attributes
188 which are not bound to a specific input or output
189 hwmon_temp Temperature sensor
190 hwmon_in Voltage sensor
191 hwmon_curr Current sensor
192 hwmon_power Power sensor
193 hwmon_energy Energy sensor
194 hwmon_humidity Humidity sensor
195 hwmon_fan Fan speed sensor
196 hwmon_pwm PWM control
197 ================== ==================================================
200 Pointer to a 0-terminated list of configuration values for each
201 sensor of the given type. Each value is a combination of bit values
202 describing the attributes supposed by a single sensor.
204 As an example, here is the complete description file for a LM75 compatible
205 sensor chip. The chip has a single temperature sensor. The driver wants to
206 register with the thermal subsystem (HWMON_C_REGISTER_TZ), and it supports
207 the update_interval attribute (HWMON_C_UPDATE_INTERVAL). The chip supports
208 reading the temperature (HWMON_T_INPUT), it has a maximum temperature
209 register (HWMON_T_MAX) as well as a maximum temperature hysteresis register
212 static const u32 lm75_chip_config[] = {
213 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL,
217 static const struct hwmon_channel_info lm75_chip = {
219 .config = lm75_chip_config,
222 static const u32 lm75_temp_config[] = {
223 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST,
227 static const struct hwmon_channel_info lm75_temp = {
229 .config = lm75_temp_config,
232 static const struct hwmon_channel_info *lm75_info[] = {
238 The HWMON_CHANNEL_INFO() macro can and should be used when possible.
239 With this macro, the above example can be simplified to
241 static const struct hwmon_channel_info *lm75_info[] = {
242 HWMON_CHANNEL_INFO(chip,
243 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL),
244 HWMON_CHANNEL_INFO(temp,
245 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST),
249 The remaining declarations are as follows.
251 static const struct hwmon_ops lm75_hwmon_ops = {
252 .is_visible = lm75_is_visible,
257 static const struct hwmon_chip_info lm75_chip_info = {
258 .ops = &lm75_hwmon_ops,
262 A complete list of bit values indicating individual attribute support
263 is defined in include/linux/hwmon.h. Definition prefixes are as follows.
265 =============== =================================================
266 HWMON_C_xxxx Chip attributes, for use with hwmon_chip.
267 HWMON_T_xxxx Temperature attributes, for use with hwmon_temp.
268 HWMON_I_xxxx Voltage attributes, for use with hwmon_in.
269 HWMON_C_xxxx Current attributes, for use with hwmon_curr.
270 Notice the prefix overlap with chip attributes.
271 HWMON_P_xxxx Power attributes, for use with hwmon_power.
272 HWMON_E_xxxx Energy attributes, for use with hwmon_energy.
273 HWMON_H_xxxx Humidity attributes, for use with hwmon_humidity.
274 HWMON_F_xxxx Fan speed attributes, for use with hwmon_fan.
275 HWMON_PWM_xxxx PWM control attributes, for use with hwmon_pwm.
276 =============== =================================================
278 Driver callback functions
279 -------------------------
281 Each driver provides is_visible, read, and write functions. Parameters
282 and return values for those functions are as follows::
284 umode_t is_visible_func(const void *data, enum hwmon_sensor_types type,
285 u32 attr, int channel)
289 Pointer to device private data structure.
293 Attribute identifier associated with a specific attribute.
294 For example, the attribute value for HWMON_T_INPUT would be
295 hwmon_temp_input. For complete mappings of bit fields to
296 attribute values please see include/linux/hwmon.h.
298 The sensor channel number.
301 The file mode for this attribute. Typically, this will be 0 (the
302 attribute will not be created), S_IRUGO, or 'S_IRUGO | S_IWUSR'.
306 int read_func(struct device *dev, enum hwmon_sensor_types type,
307 u32 attr, int channel, long *val)
311 Pointer to the hardware monitoring device.
315 Attribute identifier associated with a specific attribute.
316 For example, the attribute value for HWMON_T_INPUT would be
317 hwmon_temp_input. For complete mappings please see
318 include/linux/hwmon.h.
320 The sensor channel number.
322 Pointer to attribute value.
325 0 on success, a negative error number otherwise.
329 int write_func(struct device *dev, enum hwmon_sensor_types type,
330 u32 attr, int channel, long val)
334 Pointer to the hardware monitoring device.
338 Attribute identifier associated with a specific attribute.
339 For example, the attribute value for HWMON_T_INPUT would be
340 hwmon_temp_input. For complete mappings please see
341 include/linux/hwmon.h.
343 The sensor channel number.
345 The value to write to the chip.
348 0 on success, a negative error number otherwise.
351 Driver-provided sysfs attributes
352 --------------------------------
354 If the hardware monitoring device is registered with
355 hwmon_device_register_with_info or devm_hwmon_device_register_with_info,
356 it is most likely not necessary to provide sysfs attributes. Only additional
357 non-standard sysfs attributes need to be provided when one of those registration
360 The header file linux/hwmon-sysfs.h provides a number of useful macros to
361 declare and use hardware monitoring sysfs attributes.
363 In many cases, you can use the exsting define DEVICE_ATTR or its variants
364 DEVICE_ATTR_{RW,RO,WO} to declare such attributes. This is feasible if an
365 attribute has no additional context. However, in many cases there will be
366 additional information such as a sensor index which will need to be passed
367 to the sysfs attribute handling function.
369 SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes
370 which need such additional context information. SENSOR_DEVICE_ATTR requires
371 one additional argument, SENSOR_DEVICE_ATTR_2 requires two.
373 Simplified variants of SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 are available
374 and should be used if standard attribute permissions and function names are
375 feasible. Standard permissions are 0644 for SENSOR_DEVICE_ATTR[_2]_RW,
376 0444 for SENSOR_DEVICE_ATTR[_2]_RO, and 0200 for SENSOR_DEVICE_ATTR[_2]_WO.
377 Standard functions, similar to DEVICE_ATTR_{RW,RO,WO}, have _show and _store
378 appended to the provided function name.
380 SENSOR_DEVICE_ATTR and its variants define a struct sensor_device_attribute
381 variable. This structure has the following fields::
383 struct sensor_device_attribute {
384 struct device_attribute dev_attr;
388 You can use to_sensor_dev_attr to get the pointer to this structure from the
389 attribute read or write function. Its parameter is the device to which the
390 attribute is attached.
392 SENSOR_DEVICE_ATTR_2 and its variants define a struct sensor_device_attribute_2
393 variable, which is defined as follows::
395 struct sensor_device_attribute_2 {
396 struct device_attribute dev_attr;
401 Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter
402 is the device to which the attribute is attached.