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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.
16
17For additional guidelines on how to write and improve hwmon drivers, please
18also read Documentation/hwmon/submitting-patches.
19
20The API
21-------
22Each hardware monitoring driver must #include <linux/hwmon.h> and, in most
23cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following
24register/unregister functions:
25
26struct device *
27hwmon_device_register_with_groups(struct device *dev, const char *name,
28 void *drvdata,
29 const struct attribute_group **groups);
30
31struct device *
32devm_hwmon_device_register_with_groups(struct device *dev,
33 const char *name, void *drvdata,
34 const struct attribute_group **groups);
35
36struct device *
37hwmon_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);
41
42struct device *
43devm_hwmon_device_register_with_info(struct device *dev,
44 const char *name,
45 void *drvdata,
46 const struct hwmon_chip_info *info,
47 const struct attribute_group **extra_groups);
48
49void hwmon_device_unregister(struct device *dev);
50void devm_hwmon_device_unregister(struct device *dev);
51
52hwmon_device_register_with_groups registers a hardware monitoring device.
53The first parameter of this function is a pointer to the parent device.
54The name parameter is a pointer to the hwmon device name. The registration
55function wil create a name sysfs attribute pointing to this name.
56The drvdata parameter is the pointer to the local driver data.
57hwmon_device_register_with_groups will attach this pointer to the newly
58allocated hwmon device. The pointer can be retrieved by the driver using
59dev_get_drvdata() on the hwmon device pointer. The groups parameter is
60a pointer to a list of sysfs attribute groups. The list must be NULL terminated.
61hwmon_device_register_with_groups creates the hwmon device with name attribute
62as well as all sysfs attributes attached to the hwmon device.
63This function returns a pointer to the newly created hardware monitoring device
64or PTR_ERR for failure.
65
66devm_hwmon_device_register_with_groups is similar to
67hwmon_device_register_with_groups. However, it is device managed, meaning the
68hwmon device does not have to be removed explicitly by the removal function.
69
70hwmon_device_register_with_info is the most comprehensive and preferred means
71to register a hardware monitoring device. It creates the standard sysfs
72attributes in the hardware monitoring core, letting the driver focus on reading
73from and writing to the chip instead of having to bother with sysfs attributes.
74Its parameters are described in more detail below.
75
76devm_hwmon_device_register_with_info is similar to
77hwmon_device_register_with_info. However, it is device managed, meaning the
78hwmon device does not have to be removed explicitly by the removal function.
79
80hwmon_device_unregister deregisters a registered hardware monitoring device.
81The parameter of this function is the pointer to the registered hardware
82monitoring device structure. This function must be called from the driver
83remove function if the hardware monitoring device was registered with
84hwmon_device_register_with_groups or hwmon_device_register_with_info.
85
86devm_hwmon_device_unregister does not normally have to be called. It is only
87needed for error handling, and only needed if the driver probe fails after
88the call to devm_hwmon_device_register_with_groups or
89hwmon_device_register_with_info and if the automatic (device managed)
90removal would be too late.
91
92Using devm_hwmon_device_register_with_info()
93--------------------------------------------
94
95hwmon_device_register_with_info() registers a hardware monitoring device.
96The parameters to this function are
97
98struct device *dev Pointer to parent device
99const char *name Device name
100void *drvdata Driver private data
101const struct hwmon_chip_info *info
102 Pointer to chip description.
103const struct attribute_group **extra_groups
104 Null-terminated list of additional non-standard
105 sysfs attribute groups.
106
107This function returns a pointer to the created hardware monitoring device
108on success and a negative error code for failure.
109
110The hwmon_chip_info structure looks as follows.
111
112struct hwmon_chip_info {
113 const struct hwmon_ops *ops;
114 const struct hwmon_channel_info **info;
115};
116
117It contains the following fields:
118
119* ops: Pointer to device operations.
120* info: NULL-terminated list of device channel descriptors.
121
122The list of hwmon operations is defined as:
123
124struct hwmon_ops {
125 umode_t (*is_visible)(const void *, enum hwmon_sensor_types type,
126 u32 attr, int);
127 int (*read)(struct device *, enum hwmon_sensor_types type,
128 u32 attr, int, long *);
129 int (*write)(struct device *, enum hwmon_sensor_types type,
130 u32 attr, int, long);
131};
132
133It defines the following operations.
134
135* is_visible: Pointer to a function to return the file mode for each supported
136 attribute. This function is mandatory.
137
138* read: Pointer to a function for reading a value from the chip. This function
139 is optional, but must be provided if any readable attributes exist.
140
141* write: Pointer to a function for writing a value to the chip. This function is
142 optional, but must be provided if any writeable attributes exist.
143
144Each sensor channel is described with struct hwmon_channel_info, which is
145defined as follows.
146
147struct hwmon_channel_info {
148 enum hwmon_sensor_types type;
149 u32 *config;
150};
151
152It contains following fields:
153
154* type: The hardware monitoring sensor type.
155 Supported sensor types are
156 * hwmon_chip A virtual sensor type, used to describe attributes
157 * which are not bound to a specific input or output
158 * hwmon_temp Temperature sensor
159 * hwmon_in Voltage sensor
160 * hwmon_curr Current sensor
161 * hwmon_power Power sensor
162 * hwmon_energy Energy sensor
163 * hwmon_humidity Humidity sensor
164 * hwmon_fan Fan speed sensor
165 * hwmon_pwm PWM control
166
167* config: 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
179static const u32 lm75_chip_config[] = {
180 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL,
181 0
182};
183
184static const struct hwmon_channel_info lm75_chip = {
185 .type = hwmon_chip,
186 .config = lm75_chip_config,
187};
188
189static const u32 lm75_temp_config[] = {
190 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST,
191 0
192};
193
194static const struct hwmon_channel_info lm75_temp = {
195 .type = hwmon_temp,
196 .config = lm75_temp_config,
197};
198
199static const struct hwmon_channel_info *lm75_info[] = {
200 &lm75_chip,
201 &lm75_temp,
202 NULL
203};
204
205static const struct hwmon_ops lm75_hwmon_ops = {
206 .is_visible = lm75_is_visible,
207 .read = lm75_read,
208 .write = lm75_write,
209};
210
211static const struct hwmon_chip_info lm75_chip_info = {
212 .ops = &lm75_hwmon_ops,
213 .info = lm75_info,
214};
215
216A complete list of bit values indicating individual attribute support
217is defined in include/linux/hwmon.h. Definition prefixes are as follows.
218
219HWMON_C_xxxx Chip attributes, for use with hwmon_chip.
220HWMON_T_xxxx Temperature attributes, for use with hwmon_temp.
221HWMON_I_xxxx Voltage attributes, for use with hwmon_in.
222HWMON_C_xxxx Current attributes, for use with hwmon_curr.
223 Notice the prefix overlap with chip attributes.
224HWMON_P_xxxx Power attributes, for use with hwmon_power.
225HWMON_E_xxxx Energy attributes, for use with hwmon_energy.
226HWMON_H_xxxx Humidity attributes, for use with hwmon_humidity.
227HWMON_F_xxxx Fan speed attributes, for use with hwmon_fan.
228HWMON_PWM_xxxx PWM control attributes, for use with hwmon_pwm.
229
230Driver callback functions
231-------------------------
232
233Each driver provides is_visible, read, and write functions. Parameters
234and return values for those functions are as follows.
235
236umode_t is_visible_func(const void *data, enum hwmon_sensor_types type,
237 u32 attr, int channel)
238
239Parameters:
240 data: Pointer to device private data structure.
241 type: The sensor type.
242 attr: Attribute identifier associated with a specific attribute.
243 For example, the attribute value for HWMON_T_INPUT would be
244 hwmon_temp_input. For complete mappings of bit fields to
245 attribute values please see include/linux/hwmon.h.
246 channel:The sensor channel number.
247
248Return value:
249 The file mode for this attribute. Typically, this will be 0 (the
250 attribute will not be created), S_IRUGO, or 'S_IRUGO | S_IWUSR'.
251
252int read_func(struct device *dev, enum hwmon_sensor_types type,
253 u32 attr, int channel, long *val)
254
255Parameters:
256 dev: Pointer to the hardware monitoring device.
257 type: The sensor type.
258 attr: Attribute identifier associated with a specific attribute.
259 For example, the attribute value for HWMON_T_INPUT would be
260 hwmon_temp_input. For complete mappings please see
261 include/linux/hwmon.h.
262 channel:The sensor channel number.
263 val: Pointer to attribute value.
264
265Return value:
266 0 on success, a negative error number otherwise.
267
268int write_func(struct device *dev, enum hwmon_sensor_types type,
269 u32 attr, int channel, long val)
270
271Parameters:
272 dev: Pointer to the hardware monitoring device.
273 type: The sensor type.
274 attr: Attribute identifier associated with a specific attribute.
275 For example, the attribute value for HWMON_T_INPUT would be
276 hwmon_temp_input. For complete mappings please see
277 include/linux/hwmon.h.
278 channel:The sensor channel number.
279 val: The value to write to the chip.
280
281Return value:
282 0 on success, a negative error number otherwise.
283
284
285Driver-provided sysfs attributes
286--------------------------------
287
288If the hardware monitoring device is registered with
289hwmon_device_register_with_info or devm_hwmon_device_register_with_info,
290it is most likely not necessary to provide sysfs attributes. Only additional
291non-standard sysfs attributes need to be provided when one of those registration
292functions is used.
293
294The header file linux/hwmon-sysfs.h provides a number of useful macros to
295declare and use hardware monitoring sysfs attributes.
296
297In many cases, you can use the exsting define DEVICE_ATTR to declare such
298attributes. This is feasible if an attribute has no additional context. However,
299in many cases there will be additional information such as a sensor index which
300will need to be passed to the sysfs attribute handling function.
301
302SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes
303which need such additional context information. SENSOR_DEVICE_ATTR requires
304one additional argument, SENSOR_DEVICE_ATTR_2 requires two.
305
306SENSOR_DEVICE_ATTR defines a struct sensor_device_attribute variable.
307This structure has the following fields.
308
309struct sensor_device_attribute {
310 struct device_attribute dev_attr;
311 int index;
312};
313
314You can use to_sensor_dev_attr to get the pointer to this structure from the
315attribute read or write function. Its parameter is the device to which the
316attribute is attached.
317
318SENSOR_DEVICE_ATTR_2 defines a struct sensor_device_attribute_2 variable,
319which is defined as follows.
320
321struct sensor_device_attribute_2 {
322 struct device_attribute dev_attr;
323 u8 index;
324 u8 nr;
325};
326
327Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter
328is the device to which the attribute is attached.