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1The Linux Hardware Monitoring kernel API
2========================================
3
4Guenter Roeck
5
6Introduction
7------------
8
9This document describes the API that can be used by hardware monitoring
10drivers that want to use the hardware monitoring framework.
11
12This document does not describe what a hardware monitoring (hwmon) Driver or
13Device is. It also does not describe the API which can be used by user space
14to communicate with a hardware monitoring device. If you want to know this
15then please read the following file: Documentation/hwmon/sysfs-interface.rst.
16
17For additional guidelines on how to write and improve hwmon drivers, please
18also read Documentation/hwmon/submitting-patches.rst.
19
20The API
21-------
22Each hardware monitoring driver must #include <linux/hwmon.h> and, in some
23cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following
24register/unregister functions::
25
26 struct device *
27 hwmon_device_register_with_info(struct device *dev,
28 const char *name, void *drvdata,
29 const struct hwmon_chip_info *info,
30 const struct attribute_group **extra_groups);
31
32 struct device *
33 devm_hwmon_device_register_with_info(struct device *dev,
34 const char *name,
35 void *drvdata,
36 const struct hwmon_chip_info *info,
37 const struct attribute_group **extra_groups);
38
39 void hwmon_device_unregister(struct device *dev);
40
41 char *hwmon_sanitize_name(const char *name);
42
43 char *devm_hwmon_sanitize_name(struct device *dev, const char *name);
44
45hwmon_device_register_with_info registers a hardware monitoring device.
46It creates the standard sysfs attributes in the hardware monitoring core,
47letting the driver focus on reading from and writing to the chip instead
48of having to bother with sysfs attributes. The parent device parameter
49as well as the chip parameter must not be NULL. Its parameters are described
50in more detail below.
51
52devm_hwmon_device_register_with_info is similar to
53hwmon_device_register_with_info. However, it is device managed, meaning the
54hwmon device does not have to be removed explicitly by the removal function.
55
56All other hardware monitoring device registration functions are deprecated
57and must not be used in new drivers.
58
59hwmon_device_unregister deregisters a registered hardware monitoring device.
60The parameter of this function is the pointer to the registered hardware
61monitoring device structure. This function must be called from the driver
62remove function if the hardware monitoring device was registered with
63hwmon_device_register_with_info.
64
65All supported hwmon device registration functions only accept valid device
66names. Device names including invalid characters (whitespace, '*', or '-')
67will be rejected. The 'name' parameter is mandatory.
68
69If the driver doesn't use a static device name (for example it uses
70dev_name()), and therefore cannot make sure the name only contains valid
71characters, hwmon_sanitize_name can be used. This convenience function
72will duplicate the string and replace any invalid characters with an
73underscore. It will allocate memory for the new string and it is the
74responsibility of the caller to release the memory when the device is
75removed.
76
77devm_hwmon_sanitize_name is the resource managed version of
78hwmon_sanitize_name; the memory will be freed automatically on device
79removal.
80
81Using devm_hwmon_device_register_with_info()
82--------------------------------------------
83
84hwmon_device_register_with_info() registers a hardware monitoring device.
85The parameters to this function are
86
87=============================================== ===============================================
88`struct device *dev` Pointer to parent device
89`const char *name` Device name
90`void *drvdata` Driver private data
91`const struct hwmon_chip_info *info` Pointer to chip description.
92`const struct attribute_group **extra_groups` Null-terminated list of additional non-standard
93 sysfs attribute groups.
94=============================================== ===============================================
95
96This function returns a pointer to the created hardware monitoring device
97on success and a negative error code for failure.
98
99The hwmon_chip_info structure looks as follows::
100
101 struct hwmon_chip_info {
102 const struct hwmon_ops *ops;
103 const struct hwmon_channel_info * const *info;
104 };
105
106It contains the following fields:
107
108* ops:
109 Pointer to device operations.
110* info:
111 NULL-terminated list of device channel descriptors.
112
113The list of hwmon operations is defined as::
114
115 struct hwmon_ops {
116 umode_t (*is_visible)(const void *, enum hwmon_sensor_types type,
117 u32 attr, int);
118 int (*read)(struct device *, enum hwmon_sensor_types type,
119 u32 attr, int, long *);
120 int (*write)(struct device *, enum hwmon_sensor_types type,
121 u32 attr, int, long);
122 };
123
124It defines the following operations.
125
126* is_visible:
127 Pointer to a function to return the file mode for each supported
128 attribute. This function is mandatory.
129
130* read:
131 Pointer to a function for reading a value from the chip. This function
132 is optional, but must be provided if any readable attributes exist.
133
134* write:
135 Pointer to a function for writing a value to the chip. This function is
136 optional, but must be provided if any writeable attributes exist.
137
138Each sensor channel is described with struct hwmon_channel_info, which is
139defined as follows::
140
141 struct hwmon_channel_info {
142 enum hwmon_sensor_types type;
143 u32 *config;
144 };
145
146It contains following fields:
147
148* type:
149 The hardware monitoring sensor type.
150
151 Supported sensor types are
152
153 ================== ==================================================
154 hwmon_chip A virtual sensor type, used to describe attributes
155 which are not bound to a specific input or output
156 hwmon_temp Temperature sensor
157 hwmon_in Voltage sensor
158 hwmon_curr Current sensor
159 hwmon_power Power sensor
160 hwmon_energy Energy sensor
161 hwmon_humidity Humidity sensor
162 hwmon_fan Fan speed sensor
163 hwmon_pwm PWM control
164 ================== ==================================================
165
166* config:
167 Pointer to a 0-terminated list of configuration values for each
168 sensor of the given type. Each value is a combination of bit values
169 describing the attributes supposed by a single sensor.
170
171As an example, here is the complete description file for a LM75 compatible
172sensor chip. The chip has a single temperature sensor. The driver wants to
173register with the thermal subsystem (HWMON_C_REGISTER_TZ), and it supports
174the update_interval attribute (HWMON_C_UPDATE_INTERVAL). The chip supports
175reading the temperature (HWMON_T_INPUT), it has a maximum temperature
176register (HWMON_T_MAX) as well as a maximum temperature hysteresis register
177(HWMON_T_MAX_HYST)::
178
179 static const u32 lm75_chip_config[] = {
180 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL,
181 0
182 };
183
184 static const struct hwmon_channel_info lm75_chip = {
185 .type = hwmon_chip,
186 .config = lm75_chip_config,
187 };
188
189 static const u32 lm75_temp_config[] = {
190 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST,
191 0
192 };
193
194 static const struct hwmon_channel_info lm75_temp = {
195 .type = hwmon_temp,
196 .config = lm75_temp_config,
197 };
198
199 static const struct hwmon_channel_info * const lm75_info[] = {
200 &lm75_chip,
201 &lm75_temp,
202 NULL
203 };
204
205 The HWMON_CHANNEL_INFO() macro can and should be used when possible.
206 With this macro, the above example can be simplified to
207
208 static const struct hwmon_channel_info * const lm75_info[] = {
209 HWMON_CHANNEL_INFO(chip,
210 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL),
211 HWMON_CHANNEL_INFO(temp,
212 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST),
213 NULL
214 };
215
216 The remaining declarations are as follows.
217
218 static const struct hwmon_ops lm75_hwmon_ops = {
219 .is_visible = lm75_is_visible,
220 .read = lm75_read,
221 .write = lm75_write,
222 };
223
224 static const struct hwmon_chip_info lm75_chip_info = {
225 .ops = &lm75_hwmon_ops,
226 .info = lm75_info,
227 };
228
229A complete list of bit values indicating individual attribute support
230is defined in include/linux/hwmon.h. Definition prefixes are as follows.
231
232=============== =================================================
233HWMON_C_xxxx Chip attributes, for use with hwmon_chip.
234HWMON_T_xxxx Temperature attributes, for use with hwmon_temp.
235HWMON_I_xxxx Voltage attributes, for use with hwmon_in.
236HWMON_C_xxxx Current attributes, for use with hwmon_curr.
237 Notice the prefix overlap with chip attributes.
238HWMON_P_xxxx Power attributes, for use with hwmon_power.
239HWMON_E_xxxx Energy attributes, for use with hwmon_energy.
240HWMON_H_xxxx Humidity attributes, for use with hwmon_humidity.
241HWMON_F_xxxx Fan speed attributes, for use with hwmon_fan.
242HWMON_PWM_xxxx PWM control attributes, for use with hwmon_pwm.
243=============== =================================================
244
245Driver callback functions
246-------------------------
247
248Each driver provides is_visible, read, and write functions. Parameters
249and return values for those functions are as follows::
250
251 umode_t is_visible_func(const void *data, enum hwmon_sensor_types type,
252 u32 attr, int channel)
253
254Parameters:
255 data:
256 Pointer to device private data structure.
257 type:
258 The sensor type.
259 attr:
260 Attribute identifier associated with a specific attribute.
261 For example, the attribute value for HWMON_T_INPUT would be
262 hwmon_temp_input. For complete mappings of bit fields to
263 attribute values please see include/linux/hwmon.h.
264 channel:
265 The sensor channel number.
266
267Return value:
268 The file mode for this attribute. Typically, this will be 0 (the
269 attribute will not be created), 0444, or 0644.
270
271::
272
273 int read_func(struct device *dev, enum hwmon_sensor_types type,
274 u32 attr, int channel, long *val)
275
276Parameters:
277 dev:
278 Pointer to the hardware monitoring device.
279 type:
280 The sensor type.
281 attr:
282 Attribute identifier associated with a specific attribute.
283 For example, the attribute value for HWMON_T_INPUT would be
284 hwmon_temp_input. For complete mappings please see
285 include/linux/hwmon.h.
286 channel:
287 The sensor channel number.
288 val:
289 Pointer to attribute value.
290
291Return value:
292 0 on success, a negative error number otherwise.
293
294::
295
296 int write_func(struct device *dev, enum hwmon_sensor_types type,
297 u32 attr, int channel, long val)
298
299Parameters:
300 dev:
301 Pointer to the hardware monitoring device.
302 type:
303 The sensor type.
304 attr:
305 Attribute identifier associated with a specific attribute.
306 For example, the attribute value for HWMON_T_INPUT would be
307 hwmon_temp_input. For complete mappings please see
308 include/linux/hwmon.h.
309 channel:
310 The sensor channel number.
311 val:
312 The value to write to the chip.
313
314Return value:
315 0 on success, a negative error number otherwise.
316
317
318Driver-provided sysfs attributes
319--------------------------------
320
321In most situations it should not be necessary for a driver to provide sysfs
322attributes since the hardware monitoring core creates those internally.
323Only additional non-standard sysfs attributes need to be provided.
324
325The header file linux/hwmon-sysfs.h provides a number of useful macros to
326declare and use hardware monitoring sysfs attributes.
327
328In many cases, you can use the existing define DEVICE_ATTR or its variants
329DEVICE_ATTR_{RW,RO,WO} to declare such attributes. This is feasible if an
330attribute has no additional context. However, in many cases there will be
331additional information such as a sensor index which will need to be passed
332to the sysfs attribute handling function.
333
334SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes
335which need such additional context information. SENSOR_DEVICE_ATTR requires
336one additional argument, SENSOR_DEVICE_ATTR_2 requires two.
337
338Simplified variants of SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 are available
339and should be used if standard attribute permissions and function names are
340feasible. Standard permissions are 0644 for SENSOR_DEVICE_ATTR[_2]_RW,
3410444 for SENSOR_DEVICE_ATTR[_2]_RO, and 0200 for SENSOR_DEVICE_ATTR[_2]_WO.
342Standard functions, similar to DEVICE_ATTR_{RW,RO,WO}, have _show and _store
343appended to the provided function name.
344
345SENSOR_DEVICE_ATTR and its variants define a struct sensor_device_attribute
346variable. This structure has the following fields::
347
348 struct sensor_device_attribute {
349 struct device_attribute dev_attr;
350 int index;
351 };
352
353You can use to_sensor_dev_attr to get the pointer to this structure from the
354attribute read or write function. Its parameter is the device to which the
355attribute is attached.
356
357SENSOR_DEVICE_ATTR_2 and its variants define a struct sensor_device_attribute_2
358variable, which is defined as follows::
359
360 struct sensor_device_attribute_2 {
361 struct device_attribute dev_attr;
362 u8 index;
363 u8 nr;
364 };
365
366Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter
367is the device to which the attribute is attached.