Documentation/hwmon/hwmon-kernel-api.txt

   1 The Linux Hardware Monitoring kernel API.
   2 =========================================
   3
   4 Guenter Roeck
   5
   6 Introduction
   7 ------------
   8
   9 This document describes the API that can be used by hardware monitoring
  10 drivers that want to use the hardware monitoring framework.
  11
  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.
  16
  17 For additional guidelines on how to write and improve hwmon drivers, please
  18 also read Documentation/hwmon/submitting-patches.
  19
  20 The API
  21 -------
  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:
  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 void devm_hwmon_device_unregister(struct device *dev);
  51
  52 hwmon_device_register_with_groups registers a hardware monitoring device.
  53 The first parameter of this function is a pointer to the parent device.
  54 The name parameter is a pointer to the hwmon device name. The registration
  55 function wil create a name sysfs attribute pointing to this name.
  56 The drvdata parameter is the pointer to the local driver data.
  57 hwmon_device_register_with_groups will attach this pointer to the newly
  58 allocated hwmon device. The pointer can be retrieved by the driver using
  59 dev_get_drvdata() on the hwmon device pointer. The groups parameter is
  60 a pointer to a list of sysfs attribute groups. The list must be NULL terminated.
  61 hwmon_device_register_with_groups creates the hwmon device with name attribute
  62 as well as all sysfs attributes attached to the hwmon device.
  63 This function returns a pointer to the newly created hardware monitoring device
  64 or PTR_ERR for failure.
  65
  66 devm_hwmon_device_register_with_groups is similar to
  67 hwmon_device_register_with_groups. However, it is device managed, meaning the
  68 hwmon device does not have to be removed explicitly by the removal function.
  69
  70 hwmon_device_register_with_info is the most comprehensive and preferred means
  71 to register a hardware monitoring device. It creates the standard sysfs
  72 attributes in the hardware monitoring core, letting the driver focus on reading
  73 from and writing to the chip instead of having to bother with sysfs attributes.
  74 Its parameters are described in more detail below.
  75
  76 devm_hwmon_device_register_with_info is similar to
  77 hwmon_device_register_with_info. However, it is device managed, meaning the
  78 hwmon device does not have to be removed explicitly by the removal function.
  79
  80 hwmon_device_unregister deregisters a registered hardware monitoring device.
  81 The parameter of this function is the pointer to the registered hardware
  82 monitoring device structure. This function must be called from the driver
  83 remove function if the hardware monitoring device was registered with
  84 hwmon_device_register_with_groups or hwmon_device_register_with_info.
  85
  86 devm_hwmon_device_unregister does not normally have to be called. It is only
  87 needed for error handling, and only needed if the driver probe fails after
  88 the call to devm_hwmon_device_register_with_groups or
  89 hwmon_device_register_with_info and if the automatic (device managed)
  90 removal would be too late.
  91
  92 All supported hwmon device registration functions only accept valid device
  93 names. Device names including invalid characters (whitespace, '*', or '-')
  94 will be rejected. The 'name' parameter is mandatory.
  95
  96 Using devm_hwmon_device_register_with_info()
  97 --------------------------------------------
  98
  99 hwmon_device_register_with_info() registers a hardware monitoring device.
 100 The parameters to this function are
 101
 102 struct device *dev      Pointer to parent device
 103 const char *name        Device name
 104 void *drvdata           Driver private data
 105 const struct hwmon_chip_info *info
 106                         Pointer to chip description.
 107 const struct attribute_group **extra_groups
 108                         Null-terminated list of additional non-standard
 109                         sysfs attribute groups.
 110
 111 This function returns a pointer to the created hardware monitoring device
 112 on success and a negative error code for failure.
 113
 114 The hwmon_chip_info structure looks as follows.
 115
 116 struct hwmon_chip_info {
 117         const struct hwmon_ops *ops;
 118         const struct hwmon_channel_info **info;
 119 };
 120
 121 It contains the following fields:
 122
 123 * ops:  Pointer to device operations.
 124 * info: NULL-terminated list of device channel descriptors.
 125
 126 The list of hwmon operations is defined as:
 127
 128 struct hwmon_ops {
 129         umode_t (*is_visible)(const void *, enum hwmon_sensor_types type,
 130                               u32 attr, int);
 131         int (*read)(struct device *, enum hwmon_sensor_types type,
 132                     u32 attr, int, long *);
 133         int (*write)(struct device *, enum hwmon_sensor_types type,
 134                      u32 attr, int, long);
 135 };
 136
 137 It defines the following operations.
 138
 139 * is_visible: Pointer to a function to return the file mode for each supported
 140   attribute. This function is mandatory.
 141
 142 * read: Pointer to a function for reading a value from the chip. This function
 143   is optional, but must be provided if any readable attributes exist.
 144
 145 * write: Pointer to a function for writing a value to the chip. This function is
 146   optional, but must be provided if any writeable attributes exist.
 147
 148 Each sensor channel is described with struct hwmon_channel_info, which is
 149 defined as follows.
 150
 151 struct hwmon_channel_info {
 152         enum hwmon_sensor_types type;
 153         u32 *config;
 154 };
 155
 156 It contains following fields:
 157
 158 * type: The hardware monitoring sensor type.
 159   Supported sensor types are
 160   * hwmon_chip          A virtual sensor type, used to describe attributes
 161   *                     which are not bound to a specific input or output
 162   * hwmon_temp          Temperature sensor
 163   * hwmon_in            Voltage sensor
 164   * hwmon_curr          Current sensor
 165   * hwmon_power         Power sensor
 166   * hwmon_energy        Energy sensor
 167   * hwmon_humidity      Humidity sensor
 168   * hwmon_fan           Fan speed sensor
 169   * hwmon_pwm           PWM control
 170
 171 * config: Pointer to a 0-terminated list of configuration values for each
 172   sensor of the given type. Each value is a combination of bit values
 173   describing the attributes supposed by a single sensor.
 174
 175 As an example, here is the complete description file for a LM75 compatible
 176 sensor chip. The chip has a single temperature sensor. The driver wants to
 177 register with the thermal subsystem (HWMON_C_REGISTER_TZ), and it supports
 178 the update_interval attribute (HWMON_C_UPDATE_INTERVAL). The chip supports
 179 reading the temperature (HWMON_T_INPUT), it has a maximum temperature
 180 register (HWMON_T_MAX) as well as a maximum temperature hysteresis register
 181 (HWMON_T_MAX_HYST).
 182
 183 static const u32 lm75_chip_config[] = {
 184         HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL,
 185         0
 186 };
 187
 188 static const struct hwmon_channel_info lm75_chip = {
 189         .type = hwmon_chip,
 190         .config = lm75_chip_config,
 191 };
 192
 193 static const u32 lm75_temp_config[] = {
 194         HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST,
 195         0
 196 };
 197
 198 static const struct hwmon_channel_info lm75_temp = {
 199         .type = hwmon_temp,
 200         .config = lm75_temp_config,
 201 };
 202
 203 static const struct hwmon_channel_info *lm75_info[] = {
 204         &lm75_chip,
 205         &lm75_temp,
 206         NULL
 207 };
 208
 209 static const struct hwmon_ops lm75_hwmon_ops = {
 210         .is_visible = lm75_is_visible,
 211         .read = lm75_read,
 212         .write = lm75_write,
 213 };
 214
 215 static const struct hwmon_chip_info lm75_chip_info = {
 216         .ops = &lm75_hwmon_ops,
 217         .info = lm75_info,
 218 };
 219
 220 A complete list of bit values indicating individual attribute support
 221 is defined in include/linux/hwmon.h. Definition prefixes are as follows.
 222
 223 HWMON_C_xxxx    Chip attributes, for use with hwmon_chip.
 224 HWMON_T_xxxx    Temperature attributes, for use with hwmon_temp.
 225 HWMON_I_xxxx    Voltage attributes, for use with hwmon_in.
 226 HWMON_C_xxxx    Current attributes, for use with hwmon_curr.
 227                 Notice the prefix overlap with chip attributes.
 228 HWMON_P_xxxx    Power attributes, for use with hwmon_power.
 229 HWMON_E_xxxx    Energy attributes, for use with hwmon_energy.
 230 HWMON_H_xxxx    Humidity attributes, for use with hwmon_humidity.
 231 HWMON_F_xxxx    Fan speed attributes, for use with hwmon_fan.
 232 HWMON_PWM_xxxx  PWM control attributes, for use with hwmon_pwm.
 233
 234 Driver callback functions
 235 -------------------------
 236
 237 Each driver provides is_visible, read, and write functions. Parameters
 238 and return values for those functions are as follows.
 239
 240 umode_t is_visible_func(const void *data, enum hwmon_sensor_types type,
 241                         u32 attr, int channel)
 242
 243 Parameters:
 244         data:   Pointer to device private data structure.
 245         type:   The sensor type.
 246         attr:   Attribute identifier associated with a specific attribute.
 247                 For example, the attribute value for HWMON_T_INPUT would be
 248                 hwmon_temp_input. For complete mappings of bit fields to
 249                 attribute values please see include/linux/hwmon.h.
 250         channel:The sensor channel number.
 251
 252 Return value:
 253         The file mode for this attribute. Typically, this will be 0 (the
 254         attribute will not be created), S_IRUGO, or 'S_IRUGO | S_IWUSR'.
 255
 256 int read_func(struct device *dev, enum hwmon_sensor_types type,
 257               u32 attr, int channel, long *val)
 258
 259 Parameters:
 260         dev:    Pointer to the hardware monitoring device.
 261         type:   The sensor type.
 262         attr:   Attribute identifier associated with a specific attribute.
 263                 For example, the attribute value for HWMON_T_INPUT would be
 264                 hwmon_temp_input. For complete mappings please see
 265                 include/linux/hwmon.h.
 266         channel:The sensor channel number.
 267         val:    Pointer to attribute value.
 268
 269 Return value:
 270         0 on success, a negative error number otherwise.
 271
 272 int write_func(struct device *dev, enum hwmon_sensor_types type,
 273                u32 attr, int channel, long val)
 274
 275 Parameters:
 276         dev:    Pointer to the hardware monitoring device.
 277         type:   The sensor type.
 278         attr:   Attribute identifier associated with a specific attribute.
 279                 For example, the attribute value for HWMON_T_INPUT would be
 280                 hwmon_temp_input. For complete mappings please see
 281                 include/linux/hwmon.h.
 282         channel:The sensor channel number.
 283         val:    The value to write to the chip.
 284
 285 Return value:
 286         0 on success, a negative error number otherwise.
 287
 288
 289 Driver-provided sysfs attributes
 290 --------------------------------
 291
 292 If the hardware monitoring device is registered with
 293 hwmon_device_register_with_info or devm_hwmon_device_register_with_info,
 294 it is most likely not necessary to provide sysfs attributes. Only additional
 295 non-standard sysfs attributes need to be provided when one of those registration
 296 functions is used.
 297
 298 The header file linux/hwmon-sysfs.h provides a number of useful macros to
 299 declare and use hardware monitoring sysfs attributes.
 300
 301 In many cases, you can use the exsting define DEVICE_ATTR to declare such
 302 attributes. This is feasible if an attribute has no additional context. However,
 303 in many cases there will be additional information such as a sensor index which
 304 will need to be passed to the sysfs attribute handling function.
 305
 306 SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes
 307 which need such additional context information. SENSOR_DEVICE_ATTR requires
 308 one additional argument, SENSOR_DEVICE_ATTR_2 requires two.
 309
 310 SENSOR_DEVICE_ATTR defines a struct sensor_device_attribute variable.
 311 This structure has the following fields.
 312
 313 struct sensor_device_attribute {
 314         struct device_attribute dev_attr;
 315         int index;
 316 };
 317
 318 You can use to_sensor_dev_attr to get the pointer to this structure from the
 319 attribute read or write function. Its parameter is the device to which the
 320 attribute is attached.
 321
 322 SENSOR_DEVICE_ATTR_2 defines a struct sensor_device_attribute_2 variable,
 323 which is defined as follows.
 324
 325 struct sensor_device_attribute_2 {
 326         struct device_attribute dev_attr;
 327         u8 index;
 328         u8 nr;
 329 };
 330
 331 Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter
 332 is the device to which the attribute is attached.