Documentation/hwmon/sysfs-interface

   1 Naming and data format standards for sysfs files
   2 ------------------------------------------------
   3
   4 The libsensors library offers an interface to the raw sensors data
   5 through the sysfs interface. See libsensors documentation and source for
   6 further information. As of writing this document, libsensors
   7 (from lm_sensors 2.8.3) is heavily chip-dependent. Adding or updating
   8 support for any given chip requires modifying the library's code.
   9 This is because libsensors was written for the procfs interface
  10 older kernel modules were using, which wasn't standardized enough.
  11 Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
  12 support for the sysfs interface, though.
  13
  14 The new sysfs interface was designed to be as chip-independent as
  15 possible.
  16
  17 Note that motherboards vary widely in the connections to sensor chips.
  18 There is no standard that ensures, for example, that the second
  19 temperature sensor is connected to the CPU, or that the second fan is on
  20 the CPU. Also, some values reported by the chips need some computation
  21 before they make full sense. For example, most chips can only measure
  22 voltages between 0 and +4V. Other voltages are scaled back into that
  23 range using external resistors. Since the values of these resistors
  24 can change from motherboard to motherboard, the conversions cannot be
  25 hard coded into the driver and have to be done in user space.
  26
  27 For this reason, even if we aim at a chip-independent libsensors, it will
  28 still require a configuration file (e.g. /etc/sensors.conf) for proper
  29 values conversion, labeling of inputs and hiding of unused inputs.
  30
  31 An alternative method that some programs use is to access the sysfs
  32 files directly. This document briefly describes the standards that the
  33 drivers follow, so that an application program can scan for entries and
  34 access this data in a simple and consistent way. That said, such programs
  35 will have to implement conversion, labeling and hiding of inputs. For
  36 this reason, it is still not recommended to bypass the library.
  37
  38 If you are developing a userspace application please send us feedback on
  39 this standard.
  40
  41 Note that this standard isn't completely established yet, so it is subject
  42 to changes. If you are writing a new hardware monitoring driver those
  43 features can't seem to fit in this interface, please contact us with your
  44 extension proposal. Keep in mind that backward compatibility must be
  45 preserved.
  46
  47 Each chip gets its own directory in the sysfs /sys/devices tree.  To
  48 find all sensor chips, it is easier to follow the device symlinks from
  49 /sys/class/hwmon/hwmon*.
  50
  51 All sysfs values are fixed point numbers.
  52
  53 There is only one value per file, unlike the older /proc specification.
  54 The common scheme for files naming is: <type><number>_<item>. Usual
  55 types for sensor chips are "in" (voltage), "temp" (temperature) and
  56 "fan" (fan). Usual items are "input" (measured value), "max" (high
  57 threshold, "min" (low threshold). Numbering usually starts from 1,
  58 except for voltages which start from 0 (because most data sheets use
  59 this). A number is always used for elements that can be present more
  60 than once, even if there is a single element of the given type on the
  61 specific chip. Other files do not refer to a specific element, so
  62 they have a simple name, and no number.
  63
  64 Alarms are direct indications read from the chips. The drivers do NOT
  65 make comparisons of readings to thresholds. This allows violations
  66 between readings to be caught and alarmed. The exact definition of an
  67 alarm (for example, whether a threshold must be met or must be exceeded
  68 to cause an alarm) is chip-dependent.
  69
  70
  71 -------------------------------------------------------------------------
  72
  73 [0-*]   denotes any positive number starting from 0
  74 [1-*]   denotes any positive number starting from 1
  75 RO      read only value
  76 RW      read/write value
  77
  78 Read/write values may be read-only for some chips, depending on the
  79 hardware implementation.
  80
  81 All entries are optional, and should only be created in a given driver
  82 if the chip has the feature.
  83
  84 ************
  85 * Voltages *
  86 ************
  87
  88 in[0-*]_min     Voltage min value.
  89                 Unit: millivolt
  90                 RW
  91
  92 in[0-*]_max     Voltage max value.
  93                 Unit: millivolt
  94                 RW
  95
  96 in[0-*]_input   Voltage input value.
  97                 Unit: millivolt
  98                 RO
  99                 Voltage measured on the chip pin.
 100                 Actual voltage depends on the scaling resistors on the
 101                 motherboard, as recommended in the chip datasheet.
 102                 This varies by chip and by motherboard.
 103                 Because of this variation, values are generally NOT scaled
 104                 by the chip driver, and must be done by the application.
 105                 However, some drivers (notably lm87 and via686a)
 106                 do scale, because of internal resistors built into a chip.
 107                 These drivers will output the actual voltage.
 108
 109                 Typical usage:
 110                         in0_*   CPU #1 voltage (not scaled)
 111                         in1_*   CPU #2 voltage (not scaled)
 112                         in2_*   3.3V nominal (not scaled)
 113                         in3_*   5.0V nominal (scaled)
 114                         in4_*   12.0V nominal (scaled)
 115                         in5_*   -12.0V nominal (scaled)
 116                         in6_*   -5.0V nominal (scaled)
 117                         in7_*   varies
 118                         in8_*   varies
 119
 120 cpu[0-*]_vid    CPU core reference voltage.
 121                 Unit: millivolt
 122                 RO
 123                 Not always correct.
 124
 125 vrm             Voltage Regulator Module version number.
 126                 RW (but changing it should no more be necessary)
 127                 Originally the VRM standard version multiplied by 10, but now
 128                 an arbitrary number, as not all standards have a version
 129                 number.
 130                 Affects the way the driver calculates the CPU core reference
 131                 voltage from the vid pins.
 132
 133 Also see the Alarms section for status flags associated with voltages.
 134
 135
 136 ********
 137 * Fans *
 138 ********
 139
 140 fan[1-*]_min    Fan minimum value
 141                 Unit: revolution/min (RPM)
 142                 RW
 143
 144 fan[1-*]_input  Fan input value.
 145                 Unit: revolution/min (RPM)
 146                 RO
 147
 148 fan[1-*]_div    Fan divisor.
 149                 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
 150                 RW
 151                 Some chips only support values 1, 2, 4 and 8.
 152                 Note that this is actually an internal clock divisor, which
 153                 affects the measurable speed range, not the read value.
 154
 155 Also see the Alarms section for status flags associated with fans.
 156
 157
 158 *******
 159 * PWM *
 160 *******
 161
 162 pwm[1-*]        Pulse width modulation fan control.
 163                 Integer value in the range 0 to 255
 164                 RW
 165                 255 is max or 100%.
 166
 167 pwm[1-*]_enable
 168                 Switch PWM on and off.
 169                 Not always present even if fan*_pwm is.
 170                 0: turn off
 171                 1: turn on in manual mode
 172                 2+: turn on in automatic mode
 173                 Check individual chip documentation files for automatic mode details.
 174                 RW
 175
 176 pwm[1-*]_mode
 177                 0: DC mode
 178                 1: PWM mode
 179                 RW
 180
 181 pwm[1-*]_auto_channels_temp
 182                 Select which temperature channels affect this PWM output in
 183                 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
 184                 Which values are possible depend on the chip used.
 185                 RW
 186
 187 pwm[1-*]_auto_point[1-*]_pwm
 188 pwm[1-*]_auto_point[1-*]_temp
 189 pwm[1-*]_auto_point[1-*]_temp_hyst
 190                 Define the PWM vs temperature curve. Number of trip points is
 191                 chip-dependent. Use this for chips which associate trip points
 192                 to PWM output channels.
 193                 RW
 194
 195 OR
 196
 197 temp[1-*]_auto_point[1-*]_pwm
 198 temp[1-*]_auto_point[1-*]_temp
 199 temp[1-*]_auto_point[1-*]_temp_hyst
 200                 Define the PWM vs temperature curve. Number of trip points is
 201                 chip-dependent. Use this for chips which associate trip points
 202                 to temperature channels.
 203                 RW
 204
 205
 206 ****************
 207 * Temperatures *
 208 ****************
 209
 210 temp[1-*]_type  Sensor type selection.
 211                 Integers 1 to 4 or thermistor Beta value (typically 3435)
 212                 RW
 213                 1: PII/Celeron Diode
 214                 2: 3904 transistor
 215                 3: thermal diode
 216                 4: thermistor (default/unknown Beta)
 217                 Not all types are supported by all chips
 218
 219 temp[1-*]_max   Temperature max value.
 220                 Unit: millidegree Celsius (or millivolt, see below)
 221                 RW
 222
 223 temp[1-*]_min   Temperature min value.
 224                 Unit: millidegree Celsius
 225                 RW
 226
 227 temp[1-*]_max_hyst
 228                 Temperature hysteresis value for max limit.
 229                 Unit: millidegree Celsius
 230                 Must be reported as an absolute temperature, NOT a delta
 231                 from the max value.
 232                 RW
 233
 234 temp[1-*]_input Temperature input value.
 235                 Unit: millidegree Celsius
 236                 RO
 237
 238 temp[1-*]_crit  Temperature critical value, typically greater than
 239                 corresponding temp_max values.
 240                 Unit: millidegree Celsius
 241                 RW
 242
 243 temp[1-*]_crit_hyst
 244                 Temperature hysteresis value for critical limit.
 245                 Unit: millidegree Celsius
 246                 Must be reported as an absolute temperature, NOT a delta
 247                 from the critical value.
 248                 RW
 249
 250 temp[1-4]_offset
 251                 Temperature offset which is added to the temperature reading
 252                 by the chip.
 253                 Unit: millidegree Celsius
 254                 Read/Write value.
 255
 256                 If there are multiple temperature sensors, temp1_* is
 257                 generally the sensor inside the chip itself,
 258                 reported as "motherboard temperature".  temp2_* to
 259                 temp4_* are generally sensors external to the chip
 260                 itself, for example the thermal diode inside the CPU or
 261                 a thermistor nearby.
 262
 263 Some chips measure temperature using external thermistors and an ADC, and
 264 report the temperature measurement as a voltage. Converting this voltage
 265 back to a temperature (or the other way around for limits) requires
 266 mathematical functions not available in the kernel, so the conversion
 267 must occur in user space. For these chips, all temp* files described
 268 above should contain values expressed in millivolt instead of millidegree
 269 Celsius. In other words, such temperature channels are handled as voltage
 270 channels by the driver.
 271
 272 Also see the Alarms section for status flags associated with temperatures.
 273
 274
 275 ************
 276 * Currents *
 277 ************
 278
 279 Note that no known chip provides current measurements as of writing,
 280 so this part is theoretical, so to say.
 281
 282 curr[1-*]_max   Current max value
 283                 Unit: milliampere
 284                 RW
 285
 286 curr[1-*]_min   Current min value.
 287                 Unit: milliampere
 288                 RW
 289
 290 curr[1-*]_input Current input value
 291                 Unit: milliampere
 292                 RO
 293
 294
 295 **********
 296 * Alarms *
 297 **********
 298
 299 Each channel or limit may have an associated alarm file, containing a
 300 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
 301
 302 Usually a given chip will either use channel-related alarms, or
 303 limit-related alarms, not both. The driver should just reflect the hardware
 304 implementation.
 305
 306 in[0-*]_alarm
 307 fan[1-*]_alarm
 308 temp[1-*]_alarm
 309                 Channel alarm
 310                 0: no alarm
 311                 1: alarm
 312                 RO
 313
 314 OR
 315
 316 in[0-*]_min_alarm
 317 in[0-*]_max_alarm
 318 fan[1-*]_min_alarm
 319 temp[1-*]_min_alarm
 320 temp[1-*]_max_alarm
 321 temp[1-*]_crit_alarm
 322                 Limit alarm
 323                 0: no alarm
 324                 1: alarm
 325                 RO
 326
 327 Each input channel may have an associated fault file. This can be used
 328 to notify open diodes, unconnected fans etc. where the hardware
 329 supports it. When this boolean has value 1, the measurement for that
 330 channel should not be trusted.
 331
 332 in[0-*]_input_fault
 333 fan[1-*]_input_fault
 334 temp[1-*]_input_fault
 335                 Input fault condition
 336                 0: no fault occured
 337                 1: fault condition
 338                 RO
 339
 340 Some chips also offer the possibility to get beeped when an alarm occurs:
 341
 342 beep_enable     Master beep enable
 343                 0: no beeps
 344                 1: beeps
 345                 RW
 346
 347 in[0-*]_beep
 348 fan[1-*]_beep
 349 temp[1-*]_beep
 350                 Channel beep
 351                 0: disable
 352                 1: enable
 353                 RW
 354
 355 In theory, a chip could provide per-limit beep masking, but no such chip
 356 was seen so far.
 357
 358 Old drivers provided a different, non-standard interface to alarms and
 359 beeps. These interface files are deprecated, but will be kept around
 360 for compatibility reasons:
 361
 362 alarms          Alarm bitmask.
 363                 RO
 364                 Integer representation of one to four bytes.
 365                 A '1' bit means an alarm.
 366                 Chips should be programmed for 'comparator' mode so that
 367                 the alarm will 'come back' after you read the register
 368                 if it is still valid.
 369                 Generally a direct representation of a chip's internal
 370                 alarm registers; there is no standard for the position
 371                 of individual bits. For this reason, the use of this
 372                 interface file for new drivers is discouraged. Use
 373                 individual *_alarm and *_fault files instead.
 374                 Bits are defined in kernel/include/sensors.h.
 375
 376 beep_mask       Bitmask for beep.
 377                 Same format as 'alarms' with the same bit locations,
 378                 use discouraged for the same reason. Use individual
 379                 *_beep files instead.
 380                 RW
 381
 382
 383 *********
 384 * Other *
 385 *********
 386
 387 eeprom          Raw EEPROM data in binary form.
 388                 RO
 389
 390 pec             Enable or disable PEC (SMBus only)
 391                 0: disable
 392                 1: enable
 393                 RW