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 fan[1-*]_target
 156                 Desired fan speed
 157                 Unit: revolution/min (RPM)
 158                 RW
 159                 Only makes sense if the chip supports closed-loop fan speed
 160                 control based on the measured fan speed.
 161
 162 Also see the Alarms section for status flags associated with fans.
 163
 164
 165 *******
 166 * PWM *
 167 *******
 168
 169 pwm[1-*]        Pulse width modulation fan control.
 170                 Integer value in the range 0 to 255
 171                 RW
 172                 255 is max or 100%.
 173
 174 pwm[1-*]_enable
 175                 Switch PWM on and off.
 176                 Not always present even if pwmN is.
 177                 0: turn off
 178                 1: turn on in manual mode
 179                 2+: turn on in automatic mode
 180                 Check individual chip documentation files for automatic mode
 181                 details.
 182                 RW
 183
 184 pwm[1-*]_mode   0: DC mode (direct current)
 185                 1: PWM mode (pulse-width modulation)
 186                 RW
 187
 188 pwm[1-*]_freq   Base PWM frequency in Hz.
 189                 Only possibly available when pwmN_mode is PWM, but not always
 190                 present even then.
 191                 RW
 192
 193 pwm[1-*]_auto_channels_temp
 194                 Select which temperature channels affect this PWM output in
 195                 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
 196                 Which values are possible depend on the chip used.
 197                 RW
 198
 199 pwm[1-*]_auto_point[1-*]_pwm
 200 pwm[1-*]_auto_point[1-*]_temp
 201 pwm[1-*]_auto_point[1-*]_temp_hyst
 202                 Define the PWM vs temperature curve. Number of trip points is
 203                 chip-dependent. Use this for chips which associate trip points
 204                 to PWM output channels.
 205                 RW
 206
 207 OR
 208
 209 temp[1-*]_auto_point[1-*]_pwm
 210 temp[1-*]_auto_point[1-*]_temp
 211 temp[1-*]_auto_point[1-*]_temp_hyst
 212                 Define the PWM vs temperature curve. Number of trip points is
 213                 chip-dependent. Use this for chips which associate trip points
 214                 to temperature channels.
 215                 RW
 216
 217
 218 ****************
 219 * Temperatures *
 220 ****************
 221
 222 temp[1-*]_type  Sensor type selection.
 223                 Integers 1 to 6 or thermistor Beta value (typically 3435)
 224                 RW
 225                 1: PII/Celeron Diode
 226                 2: 3904 transistor
 227                 3: thermal diode
 228                 4: thermistor (default/unknown Beta)
 229                 5: AMD AMDSI
 230                 6: Intel PECI
 231                 Not all types are supported by all chips
 232
 233 temp[1-*]_max   Temperature max value.
 234                 Unit: millidegree Celsius (or millivolt, see below)
 235                 RW
 236
 237 temp[1-*]_min   Temperature min value.
 238                 Unit: millidegree Celsius
 239                 RW
 240
 241 temp[1-*]_max_hyst
 242                 Temperature hysteresis value for max limit.
 243                 Unit: millidegree Celsius
 244                 Must be reported as an absolute temperature, NOT a delta
 245                 from the max value.
 246                 RW
 247
 248 temp[1-*]_input Temperature input value.
 249                 Unit: millidegree Celsius
 250                 RO
 251
 252 temp[1-*]_crit  Temperature critical value, typically greater than
 253                 corresponding temp_max values.
 254                 Unit: millidegree Celsius
 255                 RW
 256
 257 temp[1-*]_crit_hyst
 258                 Temperature hysteresis value for critical limit.
 259                 Unit: millidegree Celsius
 260                 Must be reported as an absolute temperature, NOT a delta
 261                 from the critical value.
 262                 RW
 263
 264 temp[1-4]_offset
 265                 Temperature offset which is added to the temperature reading
 266                 by the chip.
 267                 Unit: millidegree Celsius
 268                 Read/Write value.
 269
 270                 If there are multiple temperature sensors, temp1_* is
 271                 generally the sensor inside the chip itself,
 272                 reported as "motherboard temperature".  temp2_* to
 273                 temp4_* are generally sensors external to the chip
 274                 itself, for example the thermal diode inside the CPU or
 275                 a thermistor nearby.
 276
 277 Some chips measure temperature using external thermistors and an ADC, and
 278 report the temperature measurement as a voltage. Converting this voltage
 279 back to a temperature (or the other way around for limits) requires
 280 mathematical functions not available in the kernel, so the conversion
 281 must occur in user space. For these chips, all temp* files described
 282 above should contain values expressed in millivolt instead of millidegree
 283 Celsius. In other words, such temperature channels are handled as voltage
 284 channels by the driver.
 285
 286 Also see the Alarms section for status flags associated with temperatures.
 287
 288
 289 ************
 290 * Currents *
 291 ************
 292
 293 Note that no known chip provides current measurements as of writing,
 294 so this part is theoretical, so to say.
 295
 296 curr[1-*]_max   Current max value
 297                 Unit: milliampere
 298                 RW
 299
 300 curr[1-*]_min   Current min value.
 301                 Unit: milliampere
 302                 RW
 303
 304 curr[1-*]_input Current input value
 305                 Unit: milliampere
 306                 RO
 307
 308
 309 **********
 310 * Alarms *
 311 **********
 312
 313 Each channel or limit may have an associated alarm file, containing a
 314 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
 315
 316 Usually a given chip will either use channel-related alarms, or
 317 limit-related alarms, not both. The driver should just reflect the hardware
 318 implementation.
 319
 320 in[0-*]_alarm
 321 fan[1-*]_alarm
 322 temp[1-*]_alarm
 323                 Channel alarm
 324                 0: no alarm
 325                 1: alarm
 326                 RO
 327
 328 OR
 329
 330 in[0-*]_min_alarm
 331 in[0-*]_max_alarm
 332 fan[1-*]_min_alarm
 333 temp[1-*]_min_alarm
 334 temp[1-*]_max_alarm
 335 temp[1-*]_crit_alarm
 336                 Limit alarm
 337                 0: no alarm
 338                 1: alarm
 339                 RO
 340
 341 Each input channel may have an associated fault file. This can be used
 342 to notify open diodes, unconnected fans etc. where the hardware
 343 supports it. When this boolean has value 1, the measurement for that
 344 channel should not be trusted.
 345
 346 in[0-*]_input_fault
 347 fan[1-*]_input_fault
 348 temp[1-*]_input_fault
 349                 Input fault condition
 350                 0: no fault occured
 351                 1: fault condition
 352                 RO
 353
 354 Some chips also offer the possibility to get beeped when an alarm occurs:
 355
 356 beep_enable     Master beep enable
 357                 0: no beeps
 358                 1: beeps
 359                 RW
 360
 361 in[0-*]_beep
 362 fan[1-*]_beep
 363 temp[1-*]_beep
 364                 Channel beep
 365                 0: disable
 366                 1: enable
 367                 RW
 368
 369 In theory, a chip could provide per-limit beep masking, but no such chip
 370 was seen so far.
 371
 372 Old drivers provided a different, non-standard interface to alarms and
 373 beeps. These interface files are deprecated, but will be kept around
 374 for compatibility reasons:
 375
 376 alarms          Alarm bitmask.
 377                 RO
 378                 Integer representation of one to four bytes.
 379                 A '1' bit means an alarm.
 380                 Chips should be programmed for 'comparator' mode so that
 381                 the alarm will 'come back' after you read the register
 382                 if it is still valid.
 383                 Generally a direct representation of a chip's internal
 384                 alarm registers; there is no standard for the position
 385                 of individual bits. For this reason, the use of this
 386                 interface file for new drivers is discouraged. Use
 387                 individual *_alarm and *_fault files instead.
 388                 Bits are defined in kernel/include/sensors.h.
 389
 390 beep_mask       Bitmask for beep.
 391                 Same format as 'alarms' with the same bit locations,
 392                 use discouraged for the same reason. Use individual
 393                 *_beep files instead.
 394                 RW
 395
 396
 397 *********
 398 * Other *
 399 *********
 400
 401 eeprom          Raw EEPROM data in binary form.
 402                 RO
 403
 404 pec             Enable or disable PEC (SMBus only)
 405                 0: disable
 406                 1: enable
 407                 RW