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 most 23cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following 24register/unregister functions:: 25 26 struct device * 27 hwmon_device_register_with_groups(struct device *dev, const char *name, 28 void *drvdata, 29 const struct attribute_group **groups); 30 31 struct device * 32 devm_hwmon_device_register_with_groups(struct device *dev, 33 const char *name, void *drvdata, 34 const struct attribute_group **groups); 35 36 struct device * 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); 41 42 struct device * 43 devm_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 49 void hwmon_device_unregister(struct device *dev); 50 51 void devm_hwmon_device_unregister(struct device *dev); 52 53hwmon_device_register_with_groups registers a hardware monitoring device. 54The first parameter of this function is a pointer to the parent device. 55The name parameter is a pointer to the hwmon device name. The registration 56function wil create a name sysfs attribute pointing to this name. 57The drvdata parameter is the pointer to the local driver data. 58hwmon_device_register_with_groups will attach this pointer to the newly 59allocated hwmon device. The pointer can be retrieved by the driver using 60dev_get_drvdata() on the hwmon device pointer. The groups parameter is 61a pointer to a list of sysfs attribute groups. The list must be NULL terminated. 62hwmon_device_register_with_groups creates the hwmon device with name attribute 63as well as all sysfs attributes attached to the hwmon device. 64This function returns a pointer to the newly created hardware monitoring device 65or PTR_ERR for failure. 66 67devm_hwmon_device_register_with_groups is similar to 68hwmon_device_register_with_groups. However, it is device managed, meaning the 69hwmon device does not have to be removed explicitly by the removal function. 70 71hwmon_device_register_with_info is the most comprehensive and preferred means 72to register a hardware monitoring device. It creates the standard sysfs 73attributes in the hardware monitoring core, letting the driver focus on reading 74from and writing to the chip instead of having to bother with sysfs attributes. 75The parent device parameter cannot be NULL with non-NULL chip info. Its 76parameters are described in more detail below. 77 78devm_hwmon_device_register_with_info is similar to 79hwmon_device_register_with_info. However, it is device managed, meaning the 80hwmon device does not have to be removed explicitly by the removal function. 81 82hwmon_device_unregister deregisters a registered hardware monitoring device. 83The parameter of this function is the pointer to the registered hardware 84monitoring device structure. This function must be called from the driver 85remove function if the hardware monitoring device was registered with 86hwmon_device_register_with_groups or hwmon_device_register_with_info. 87 88devm_hwmon_device_unregister does not normally have to be called. It is only 89needed for error handling, and only needed if the driver probe fails after 90the call to devm_hwmon_device_register_with_groups or 91hwmon_device_register_with_info and if the automatic (device managed) 92removal would be too late. 93 94All supported hwmon device registration functions only accept valid device 95names. Device names including invalid characters (whitespace, '*', or '-') 96will be rejected. The 'name' parameter is mandatory. 97 98Using devm_hwmon_device_register_with_info() 99-------------------------------------------- 100 101hwmon_device_register_with_info() registers a hardware monitoring device. 102The parameters to this function are 103 104=============================================== =============================================== 105`struct device *dev` Pointer to parent device 106`const char *name` Device name 107`void *drvdata` Driver private data 108`const struct hwmon_chip_info *info` Pointer to chip description. 109`const struct attribute_group **extra_groups` Null-terminated list of additional non-standard 110 sysfs attribute groups. 111=============================================== =============================================== 112 113This function returns a pointer to the created hardware monitoring device 114on success and a negative error code for failure. 115 116The hwmon_chip_info structure looks as follows:: 117 118 struct hwmon_chip_info { 119 const struct hwmon_ops *ops; 120 const struct hwmon_channel_info **info; 121 }; 122 123It contains the following fields: 124 125* ops: 126 Pointer to device operations. 127* info: 128 NULL-terminated list of device channel descriptors. 129 130The list of hwmon operations is defined as:: 131 132 struct hwmon_ops { 133 umode_t (*is_visible)(const void *, enum hwmon_sensor_types type, 134 u32 attr, int); 135 int (*read)(struct device *, enum hwmon_sensor_types type, 136 u32 attr, int, long *); 137 int (*write)(struct device *, enum hwmon_sensor_types type, 138 u32 attr, int, long); 139 }; 140 141It defines the following operations. 142 143* is_visible: 144 Pointer to a function to return the file mode for each supported 145 attribute. This function is mandatory. 146 147* read: 148 Pointer to a function for reading a value from the chip. This function 149 is optional, but must be provided if any readable attributes exist. 150 151* write: 152 Pointer to a function for writing a value to the chip. This function is 153 optional, but must be provided if any writeable attributes exist. 154 155Each sensor channel is described with struct hwmon_channel_info, which is 156defined as follows:: 157 158 struct hwmon_channel_info { 159 enum hwmon_sensor_types type; 160 u32 *config; 161 }; 162 163It contains following fields: 164 165* type: 166 The hardware monitoring sensor type. 167 168 Supported sensor types are 169 170 ================== ================================================== 171 hwmon_chip A virtual sensor type, used to describe attributes 172 which are not bound to a specific input or output 173 hwmon_temp Temperature sensor 174 hwmon_in Voltage sensor 175 hwmon_curr Current sensor 176 hwmon_power Power sensor 177 hwmon_energy Energy sensor 178 hwmon_humidity Humidity sensor 179 hwmon_fan Fan speed sensor 180 hwmon_pwm PWM control 181 ================== ================================================== 182 183* config: 184 Pointer to a 0-terminated list of configuration values for each 185 sensor of the given type. Each value is a combination of bit values 186 describing the attributes supposed by a single sensor. 187 188As an example, here is the complete description file for a LM75 compatible 189sensor chip. The chip has a single temperature sensor. The driver wants to 190register with the thermal subsystem (HWMON_C_REGISTER_TZ), and it supports 191the update_interval attribute (HWMON_C_UPDATE_INTERVAL). The chip supports 192reading the temperature (HWMON_T_INPUT), it has a maximum temperature 193register (HWMON_T_MAX) as well as a maximum temperature hysteresis register 194(HWMON_T_MAX_HYST):: 195 196 static const u32 lm75_chip_config[] = { 197 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL, 198 0 199 }; 200 201 static const struct hwmon_channel_info lm75_chip = { 202 .type = hwmon_chip, 203 .config = lm75_chip_config, 204 }; 205 206 static const u32 lm75_temp_config[] = { 207 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST, 208 0 209 }; 210 211 static const struct hwmon_channel_info lm75_temp = { 212 .type = hwmon_temp, 213 .config = lm75_temp_config, 214 }; 215 216 static const struct hwmon_channel_info *lm75_info[] = { 217 &lm75_chip, 218 &lm75_temp, 219 NULL 220 }; 221 222 The HWMON_CHANNEL_INFO() macro can and should be used when possible. 223 With this macro, the above example can be simplified to 224 225 static const struct hwmon_channel_info *lm75_info[] = { 226 HWMON_CHANNEL_INFO(chip, 227 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL), 228 HWMON_CHANNEL_INFO(temp, 229 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST), 230 NULL 231 }; 232 233 The remaining declarations are as follows. 234 235 static const struct hwmon_ops lm75_hwmon_ops = { 236 .is_visible = lm75_is_visible, 237 .read = lm75_read, 238 .write = lm75_write, 239 }; 240 241 static const struct hwmon_chip_info lm75_chip_info = { 242 .ops = &lm75_hwmon_ops, 243 .info = lm75_info, 244 }; 245 246A complete list of bit values indicating individual attribute support 247is defined in include/linux/hwmon.h. Definition prefixes are as follows. 248 249=============== ================================================= 250HWMON_C_xxxx Chip attributes, for use with hwmon_chip. 251HWMON_T_xxxx Temperature attributes, for use with hwmon_temp. 252HWMON_I_xxxx Voltage attributes, for use with hwmon_in. 253HWMON_C_xxxx Current attributes, for use with hwmon_curr. 254 Notice the prefix overlap with chip attributes. 255HWMON_P_xxxx Power attributes, for use with hwmon_power. 256HWMON_E_xxxx Energy attributes, for use with hwmon_energy. 257HWMON_H_xxxx Humidity attributes, for use with hwmon_humidity. 258HWMON_F_xxxx Fan speed attributes, for use with hwmon_fan. 259HWMON_PWM_xxxx PWM control attributes, for use with hwmon_pwm. 260=============== ================================================= 261 262Driver callback functions 263------------------------- 264 265Each driver provides is_visible, read, and write functions. Parameters 266and return values for those functions are as follows:: 267 268 umode_t is_visible_func(const void *data, enum hwmon_sensor_types type, 269 u32 attr, int channel) 270 271Parameters: 272 data: 273 Pointer to device private data structure. 274 type: 275 The sensor type. 276 attr: 277 Attribute identifier associated with a specific attribute. 278 For example, the attribute value for HWMON_T_INPUT would be 279 hwmon_temp_input. For complete mappings of bit fields to 280 attribute values please see include/linux/hwmon.h. 281 channel: 282 The sensor channel number. 283 284Return value: 285 The file mode for this attribute. Typically, this will be 0 (the 286 attribute will not be created), S_IRUGO, or 'S_IRUGO | S_IWUSR'. 287 288:: 289 290 int read_func(struct device *dev, enum hwmon_sensor_types type, 291 u32 attr, int channel, long *val) 292 293Parameters: 294 dev: 295 Pointer to the hardware monitoring device. 296 type: 297 The sensor type. 298 attr: 299 Attribute identifier associated with a specific attribute. 300 For example, the attribute value for HWMON_T_INPUT would be 301 hwmon_temp_input. For complete mappings please see 302 include/linux/hwmon.h. 303 channel: 304 The sensor channel number. 305 val: 306 Pointer to attribute value. 307 308Return value: 309 0 on success, a negative error number otherwise. 310 311:: 312 313 int write_func(struct device *dev, enum hwmon_sensor_types type, 314 u32 attr, int channel, long val) 315 316Parameters: 317 dev: 318 Pointer to the hardware monitoring device. 319 type: 320 The sensor type. 321 attr: 322 Attribute identifier associated with a specific attribute. 323 For example, the attribute value for HWMON_T_INPUT would be 324 hwmon_temp_input. For complete mappings please see 325 include/linux/hwmon.h. 326 channel: 327 The sensor channel number. 328 val: 329 The value to write to the chip. 330 331Return value: 332 0 on success, a negative error number otherwise. 333 334 335Driver-provided sysfs attributes 336-------------------------------- 337 338If the hardware monitoring device is registered with 339hwmon_device_register_with_info or devm_hwmon_device_register_with_info, 340it is most likely not necessary to provide sysfs attributes. Only additional 341non-standard sysfs attributes need to be provided when one of those registration 342functions is used. 343 344The header file linux/hwmon-sysfs.h provides a number of useful macros to 345declare and use hardware monitoring sysfs attributes. 346 347In many cases, you can use the exsting define DEVICE_ATTR or its variants 348DEVICE_ATTR_{RW,RO,WO} to declare such attributes. This is feasible if an 349attribute has no additional context. However, in many cases there will be 350additional information such as a sensor index which will need to be passed 351to the sysfs attribute handling function. 352 353SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes 354which need such additional context information. SENSOR_DEVICE_ATTR requires 355one additional argument, SENSOR_DEVICE_ATTR_2 requires two. 356 357Simplified variants of SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 are available 358and should be used if standard attribute permissions and function names are 359feasible. Standard permissions are 0644 for SENSOR_DEVICE_ATTR[_2]_RW, 3600444 for SENSOR_DEVICE_ATTR[_2]_RO, and 0200 for SENSOR_DEVICE_ATTR[_2]_WO. 361Standard functions, similar to DEVICE_ATTR_{RW,RO,WO}, have _show and _store 362appended to the provided function name. 363 364SENSOR_DEVICE_ATTR and its variants define a struct sensor_device_attribute 365variable. This structure has the following fields:: 366 367 struct sensor_device_attribute { 368 struct device_attribute dev_attr; 369 int index; 370 }; 371 372You can use to_sensor_dev_attr to get the pointer to this structure from the 373attribute read or write function. Its parameter is the device to which the 374attribute is attached. 375 376SENSOR_DEVICE_ATTR_2 and its variants define a struct sensor_device_attribute_2 377variable, which is defined as follows:: 378 379 struct sensor_device_attribute_2 { 380 struct device_attribute dev_attr; 381 u8 index; 382 u8 nr; 383 }; 384 385Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter 386is the device to which the attribute is attached. 387