0001 The Linux Hardware Monitoring kernel API
0002 ========================================
0003
0004 Guenter Roeck
0005
0006 Introduction
0007 ------------
0008
0009 This document describes the API that can be used by hardware monitoring
0010 drivers that want to use the hardware monitoring framework.
0011
0012 This document does not describe what a hardware monitoring (hwmon) Driver or
0013 Device is. It also does not describe the API which can be used by user space
0014 to communicate with a hardware monitoring device. If you want to know this
0015 then please read the following file: Documentation/hwmon/sysfs-interface.rst.
0016
0017 For additional guidelines on how to write and improve hwmon drivers, please
0018 also read Documentation/hwmon/submitting-patches.rst.
0019
0020 The API
0021 -------
0022 Each hardware monitoring driver must #include <linux/hwmon.h> and, in most
0023 cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following
0024 register/unregister functions::
0025
0026 struct device *
0027 hwmon_device_register_with_groups(struct device *dev, const char *name,
0028 void *drvdata,
0029 const struct attribute_group **groups);
0030
0031 struct device *
0032 devm_hwmon_device_register_with_groups(struct device *dev,
0033 const char *name, void *drvdata,
0034 const struct attribute_group **groups);
0035
0036 struct device *
0037 hwmon_device_register_with_info(struct device *dev,
0038 const char *name, void *drvdata,
0039 const struct hwmon_chip_info *info,
0040 const struct attribute_group **extra_groups);
0041
0042 struct device *
0043 devm_hwmon_device_register_with_info(struct device *dev,
0044 const char *name,
0045 void *drvdata,
0046 const struct hwmon_chip_info *info,
0047 const struct attribute_group **extra_groups);
0048
0049 void hwmon_device_unregister(struct device *dev);
0050
0051 void devm_hwmon_device_unregister(struct device *dev);
0052
0053 char *hwmon_sanitize_name(const char *name);
0054
0055 char *devm_hwmon_sanitize_name(struct device *dev, const char *name);
0056
0057 hwmon_device_register_with_groups registers a hardware monitoring device.
0058 The first parameter of this function is a pointer to the parent device.
0059 The name parameter is a pointer to the hwmon device name. The registration
0060 function wil create a name sysfs attribute pointing to this name.
0061 The drvdata parameter is the pointer to the local driver data.
0062 hwmon_device_register_with_groups will attach this pointer to the newly
0063 allocated hwmon device. The pointer can be retrieved by the driver using
0064 dev_get_drvdata() on the hwmon device pointer. The groups parameter is
0065 a pointer to a list of sysfs attribute groups. The list must be NULL terminated.
0066 hwmon_device_register_with_groups creates the hwmon device with name attribute
0067 as well as all sysfs attributes attached to the hwmon device.
0068 This function returns a pointer to the newly created hardware monitoring device
0069 or PTR_ERR for failure.
0070
0071 devm_hwmon_device_register_with_groups is similar to
0072 hwmon_device_register_with_groups. However, it is device managed, meaning the
0073 hwmon device does not have to be removed explicitly by the removal function.
0074
0075 hwmon_device_register_with_info is the most comprehensive and preferred means
0076 to register a hardware monitoring device. It creates the standard sysfs
0077 attributes in the hardware monitoring core, letting the driver focus on reading
0078 from and writing to the chip instead of having to bother with sysfs attributes.
0079 The parent device parameter as well as the chip parameter must not be NULL. Its
0080 parameters are described in more detail below.
0081
0082 devm_hwmon_device_register_with_info is similar to
0083 hwmon_device_register_with_info. However, it is device managed, meaning the
0084 hwmon device does not have to be removed explicitly by the removal function.
0085
0086 hwmon_device_unregister deregisters a registered hardware monitoring device.
0087 The parameter of this function is the pointer to the registered hardware
0088 monitoring device structure. This function must be called from the driver
0089 remove function if the hardware monitoring device was registered with
0090 hwmon_device_register_with_groups or hwmon_device_register_with_info.
0091
0092 devm_hwmon_device_unregister does not normally have to be called. It is only
0093 needed for error handling, and only needed if the driver probe fails after
0094 the call to devm_hwmon_device_register_with_groups or
0095 hwmon_device_register_with_info and if the automatic (device managed)
0096 removal would be too late.
0097
0098 All supported hwmon device registration functions only accept valid device
0099 names. Device names including invalid characters (whitespace, '*', or '-')
0100 will be rejected. The 'name' parameter is mandatory.
0101
0102 If the driver doesn't use a static device name (for example it uses
0103 dev_name()), and therefore cannot make sure the name only contains valid
0104 characters, hwmon_sanitize_name can be used. This convenience function
0105 will duplicate the string and replace any invalid characters with an
0106 underscore. It will allocate memory for the new string and it is the
0107 responsibility of the caller to release the memory when the device is
0108 removed.
0109
0110 devm_hwmon_sanitize_name is the resource managed version of
0111 hwmon_sanitize_name; the memory will be freed automatically on device
0112 removal.
0113
0114 Using devm_hwmon_device_register_with_info()
0115 --------------------------------------------
0116
0117 hwmon_device_register_with_info() registers a hardware monitoring device.
0118 The parameters to this function are
0119
0120 =============================================== ===============================================
0121 `struct device *dev` Pointer to parent device
0122 `const char *name` Device name
0123 `void *drvdata` Driver private data
0124 `const struct hwmon_chip_info *info` Pointer to chip description.
0125 `const struct attribute_group **extra_groups` Null-terminated list of additional non-standard
0126 sysfs attribute groups.
0127 =============================================== ===============================================
0128
0129 This function returns a pointer to the created hardware monitoring device
0130 on success and a negative error code for failure.
0131
0132 The hwmon_chip_info structure looks as follows::
0133
0134 struct hwmon_chip_info {
0135 const struct hwmon_ops *ops;
0136 const struct hwmon_channel_info **info;
0137 };
0138
0139 It contains the following fields:
0140
0141 * ops:
0142 Pointer to device operations.
0143 * info:
0144 NULL-terminated list of device channel descriptors.
0145
0146 The list of hwmon operations is defined as::
0147
0148 struct hwmon_ops {
0149 umode_t (*is_visible)(const void *, enum hwmon_sensor_types type,
0150 u32 attr, int);
0151 int (*read)(struct device *, enum hwmon_sensor_types type,
0152 u32 attr, int, long *);
0153 int (*write)(struct device *, enum hwmon_sensor_types type,
0154 u32 attr, int, long);
0155 };
0156
0157 It defines the following operations.
0158
0159 * is_visible:
0160 Pointer to a function to return the file mode for each supported
0161 attribute. This function is mandatory.
0162
0163 * read:
0164 Pointer to a function for reading a value from the chip. This function
0165 is optional, but must be provided if any readable attributes exist.
0166
0167 * write:
0168 Pointer to a function for writing a value to the chip. This function is
0169 optional, but must be provided if any writeable attributes exist.
0170
0171 Each sensor channel is described with struct hwmon_channel_info, which is
0172 defined as follows::
0173
0174 struct hwmon_channel_info {
0175 enum hwmon_sensor_types type;
0176 u32 *config;
0177 };
0178
0179 It contains following fields:
0180
0181 * type:
0182 The hardware monitoring sensor type.
0183
0184 Supported sensor types are
0185
0186 ================== ==================================================
0187 hwmon_chip A virtual sensor type, used to describe attributes
0188 which are not bound to a specific input or output
0189 hwmon_temp Temperature sensor
0190 hwmon_in Voltage sensor
0191 hwmon_curr Current sensor
0192 hwmon_power Power sensor
0193 hwmon_energy Energy sensor
0194 hwmon_humidity Humidity sensor
0195 hwmon_fan Fan speed sensor
0196 hwmon_pwm PWM control
0197 ================== ==================================================
0198
0199 * config:
0200 Pointer to a 0-terminated list of configuration values for each
0201 sensor of the given type. Each value is a combination of bit values
0202 describing the attributes supposed by a single sensor.
0203
0204 As an example, here is the complete description file for a LM75 compatible
0205 sensor chip. The chip has a single temperature sensor. The driver wants to
0206 register with the thermal subsystem (HWMON_C_REGISTER_TZ), and it supports
0207 the update_interval attribute (HWMON_C_UPDATE_INTERVAL). The chip supports
0208 reading the temperature (HWMON_T_INPUT), it has a maximum temperature
0209 register (HWMON_T_MAX) as well as a maximum temperature hysteresis register
0210 (HWMON_T_MAX_HYST)::
0211
0212 static const u32 lm75_chip_config[] = {
0213 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL,
0214 0
0215 };
0216
0217 static const struct hwmon_channel_info lm75_chip = {
0218 .type = hwmon_chip,
0219 .config = lm75_chip_config,
0220 };
0221
0222 static const u32 lm75_temp_config[] = {
0223 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST,
0224 0
0225 };
0226
0227 static const struct hwmon_channel_info lm75_temp = {
0228 .type = hwmon_temp,
0229 .config = lm75_temp_config,
0230 };
0231
0232 static const struct hwmon_channel_info *lm75_info[] = {
0233 &lm75_chip,
0234 &lm75_temp,
0235 NULL
0236 };
0237
0238 The HWMON_CHANNEL_INFO() macro can and should be used when possible.
0239 With this macro, the above example can be simplified to
0240
0241 static const struct hwmon_channel_info *lm75_info[] = {
0242 HWMON_CHANNEL_INFO(chip,
0243 HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL),
0244 HWMON_CHANNEL_INFO(temp,
0245 HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST),
0246 NULL
0247 };
0248
0249 The remaining declarations are as follows.
0250
0251 static const struct hwmon_ops lm75_hwmon_ops = {
0252 .is_visible = lm75_is_visible,
0253 .read = lm75_read,
0254 .write = lm75_write,
0255 };
0256
0257 static const struct hwmon_chip_info lm75_chip_info = {
0258 .ops = &lm75_hwmon_ops,
0259 .info = lm75_info,
0260 };
0261
0262 A complete list of bit values indicating individual attribute support
0263 is defined in include/linux/hwmon.h. Definition prefixes are as follows.
0264
0265 =============== =================================================
0266 HWMON_C_xxxx Chip attributes, for use with hwmon_chip.
0267 HWMON_T_xxxx Temperature attributes, for use with hwmon_temp.
0268 HWMON_I_xxxx Voltage attributes, for use with hwmon_in.
0269 HWMON_C_xxxx Current attributes, for use with hwmon_curr.
0270 Notice the prefix overlap with chip attributes.
0271 HWMON_P_xxxx Power attributes, for use with hwmon_power.
0272 HWMON_E_xxxx Energy attributes, for use with hwmon_energy.
0273 HWMON_H_xxxx Humidity attributes, for use with hwmon_humidity.
0274 HWMON_F_xxxx Fan speed attributes, for use with hwmon_fan.
0275 HWMON_PWM_xxxx PWM control attributes, for use with hwmon_pwm.
0276 =============== =================================================
0277
0278 Driver callback functions
0279 -------------------------
0280
0281 Each driver provides is_visible, read, and write functions. Parameters
0282 and return values for those functions are as follows::
0283
0284 umode_t is_visible_func(const void *data, enum hwmon_sensor_types type,
0285 u32 attr, int channel)
0286
0287 Parameters:
0288 data:
0289 Pointer to device private data structure.
0290 type:
0291 The sensor type.
0292 attr:
0293 Attribute identifier associated with a specific attribute.
0294 For example, the attribute value for HWMON_T_INPUT would be
0295 hwmon_temp_input. For complete mappings of bit fields to
0296 attribute values please see include/linux/hwmon.h.
0297 channel:
0298 The sensor channel number.
0299
0300 Return value:
0301 The file mode for this attribute. Typically, this will be 0 (the
0302 attribute will not be created), S_IRUGO, or 'S_IRUGO | S_IWUSR'.
0303
0304 ::
0305
0306 int read_func(struct device *dev, enum hwmon_sensor_types type,
0307 u32 attr, int channel, long *val)
0308
0309 Parameters:
0310 dev:
0311 Pointer to the hardware monitoring device.
0312 type:
0313 The sensor type.
0314 attr:
0315 Attribute identifier associated with a specific attribute.
0316 For example, the attribute value for HWMON_T_INPUT would be
0317 hwmon_temp_input. For complete mappings please see
0318 include/linux/hwmon.h.
0319 channel:
0320 The sensor channel number.
0321 val:
0322 Pointer to attribute value.
0323
0324 Return value:
0325 0 on success, a negative error number otherwise.
0326
0327 ::
0328
0329 int write_func(struct device *dev, enum hwmon_sensor_types type,
0330 u32 attr, int channel, long val)
0331
0332 Parameters:
0333 dev:
0334 Pointer to the hardware monitoring device.
0335 type:
0336 The sensor type.
0337 attr:
0338 Attribute identifier associated with a specific attribute.
0339 For example, the attribute value for HWMON_T_INPUT would be
0340 hwmon_temp_input. For complete mappings please see
0341 include/linux/hwmon.h.
0342 channel:
0343 The sensor channel number.
0344 val:
0345 The value to write to the chip.
0346
0347 Return value:
0348 0 on success, a negative error number otherwise.
0349
0350
0351 Driver-provided sysfs attributes
0352 --------------------------------
0353
0354 If the hardware monitoring device is registered with
0355 hwmon_device_register_with_info or devm_hwmon_device_register_with_info,
0356 it is most likely not necessary to provide sysfs attributes. Only additional
0357 non-standard sysfs attributes need to be provided when one of those registration
0358 functions is used.
0359
0360 The header file linux/hwmon-sysfs.h provides a number of useful macros to
0361 declare and use hardware monitoring sysfs attributes.
0362
0363 In many cases, you can use the exsting define DEVICE_ATTR or its variants
0364 DEVICE_ATTR_{RW,RO,WO} to declare such attributes. This is feasible if an
0365 attribute has no additional context. However, in many cases there will be
0366 additional information such as a sensor index which will need to be passed
0367 to the sysfs attribute handling function.
0368
0369 SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes
0370 which need such additional context information. SENSOR_DEVICE_ATTR requires
0371 one additional argument, SENSOR_DEVICE_ATTR_2 requires two.
0372
0373 Simplified variants of SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 are available
0374 and should be used if standard attribute permissions and function names are
0375 feasible. Standard permissions are 0644 for SENSOR_DEVICE_ATTR[_2]_RW,
0376 0444 for SENSOR_DEVICE_ATTR[_2]_RO, and 0200 for SENSOR_DEVICE_ATTR[_2]_WO.
0377 Standard functions, similar to DEVICE_ATTR_{RW,RO,WO}, have _show and _store
0378 appended to the provided function name.
0379
0380 SENSOR_DEVICE_ATTR and its variants define a struct sensor_device_attribute
0381 variable. This structure has the following fields::
0382
0383 struct sensor_device_attribute {
0384 struct device_attribute dev_attr;
0385 int index;
0386 };
0387
0388 You can use to_sensor_dev_attr to get the pointer to this structure from the
0389 attribute read or write function. Its parameter is the device to which the
0390 attribute is attached.
0391
0392 SENSOR_DEVICE_ATTR_2 and its variants define a struct sensor_device_attribute_2
0393 variable, which is defined as follows::
0394
0395 struct sensor_device_attribute_2 {
0396 struct device_attribute dev_attr;
0397 u8 index;
0398 u8 nr;
0399 };
0400
0401 Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter
0402 is the device to which the attribute is attached.
