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. Since lm-sensors 3.0.0, libsensors is
   6 completely chip-independent. It assumes that all the kernel drivers
   7 implement the standard sysfs interface described in this document.
   8 This makes adding or updating support for any given chip very easy, as
   9 libsensors, and applications using it, do not need to be modified.
  10 This is a major improvement compared to lm-sensors 2.
  11
  12 Note that motherboards vary widely in the connections to sensor chips.
  13 There is no standard that ensures, for example, that the second
  14 temperature sensor is connected to the CPU, or that the second fan is on
  15 the CPU. Also, some values reported by the chips need some computation
  16 before they make full sense. For example, most chips can only measure
  17 voltages between 0 and +4V. Other voltages are scaled back into that
  18 range using external resistors. Since the values of these resistors
  19 can change from motherboard to motherboard, the conversions cannot be
  20 hard coded into the driver and have to be done in user space.
  21
  22 For this reason, even if we aim at a chip-independent libsensors, it will
  23 still require a configuration file (e.g. /etc/sensors.conf) for proper
  24 values conversion, labeling of inputs and hiding of unused inputs.
  25
  26 An alternative method that some programs use is to access the sysfs
  27 files directly. This document briefly describes the standards that the
  28 drivers follow, so that an application program can scan for entries and
  29 access this data in a simple and consistent way. That said, such programs
  30 will have to implement conversion, labeling and hiding of inputs. For
  31 this reason, it is still not recommended to bypass the library.
  32
  33 Each chip gets its own directory in the sysfs /sys/devices tree.  To
  34 find all sensor chips, it is easier to follow the device symlinks from
  35 /sys/class/hwmon/hwmon*.
  36
  37 Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
  38 in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
  39 in the hwmon "class" device directory are also supported. Complex drivers
  40 (e.g. drivers for multifunction chips) may want to use this possibility to
  41 avoid namespace pollution. The only drawback will be that older versions of
  42 libsensors won't support the driver in question.
  43
  44 All sysfs values are fixed point numbers.
  45
  46 There is only one value per file, unlike the older /proc specification.
  47 The common scheme for files naming is: <type><number>_<item>. Usual
  48 types for sensor chips are "in" (voltage), "temp" (temperature) and
  49 "fan" (fan). Usual items are "input" (measured value), "max" (high
  50 threshold, "min" (low threshold). Numbering usually starts from 1,
  51 except for voltages which start from 0 (because most data sheets use
  52 this). A number is always used for elements that can be present more
  53 than once, even if there is a single element of the given type on the
  54 specific chip. Other files do not refer to a specific element, so
  55 they have a simple name, and no number.
  56
  57 Alarms are direct indications read from the chips. The drivers do NOT
  58 make comparisons of readings to thresholds. This allows violations
  59 between readings to be caught and alarmed. The exact definition of an
  60 alarm (for example, whether a threshold must be met or must be exceeded
  61 to cause an alarm) is chip-dependent.
  62
  63 When setting values of hwmon sysfs attributes, the string representation of
  64 the desired value must be written, note that strings which are not a number
  65 are interpreted as 0! For more on how written strings are interpreted see the
  66 "sysfs attribute writes interpretation" section at the end of this file.
  67
  68 -------------------------------------------------------------------------
  69
  70 [0-*]   denotes any positive number starting from 0
  71 [1-*]   denotes any positive number starting from 1
  72 RO      read only value
  73 RW      read/write value
  74
  75 Read/write values may be read-only for some chips, depending on the
  76 hardware implementation.
  77
  78 All entries (except name) are optional, and should only be created in a
  79 given driver if the chip has the feature.
  80
  81
  82 ********
  83 * Name *
  84 ********
  85
  86 name            The chip name.
  87                 This should be a short, lowercase string, not containing
  88                 spaces nor dashes, representing the chip name. This is
  89                 the only mandatory attribute.
  90                 I2C devices get this attribute created automatically.
  91                 RO
  92
  93
  94 ************
  95 * Voltages *
  96 ************
  97
  98 in[0-*]_min     Voltage min value.
  99                 Unit: millivolt
 100                 RW
 101
 102 in[0-*]_max     Voltage max value.
 103                 Unit: millivolt
 104                 RW
 105
 106 in[0-*]_input   Voltage input value.
 107                 Unit: millivolt
 108                 RO
 109                 Voltage measured on the chip pin.
 110                 Actual voltage depends on the scaling resistors on the
 111                 motherboard, as recommended in the chip datasheet.
 112                 This varies by chip and by motherboard.
 113                 Because of this variation, values are generally NOT scaled
 114                 by the chip driver, and must be done by the application.
 115                 However, some drivers (notably lm87 and via686a)
 116                 do scale, because of internal resistors built into a chip.
 117                 These drivers will output the actual voltage. Rule of
 118                 thumb: drivers should report the voltage values at the
 119                 "pins" of the chip.
 120
 121 in[0-*]_label   Suggested voltage channel label.
 122                 Text string
 123                 Should only be created if the driver has hints about what
 124                 this voltage channel is being used for, and user-space
 125                 doesn't. In all other cases, the label is provided by
 126                 user-space.
 127                 RO
 128
 129 cpu[0-*]_vid    CPU core reference voltage.
 130                 Unit: millivolt
 131                 RO
 132                 Not always correct.
 133
 134 vrm             Voltage Regulator Module version number.
 135                 RW (but changing it should no more be necessary)
 136                 Originally the VRM standard version multiplied by 10, but now
 137                 an arbitrary number, as not all standards have a version
 138                 number.
 139                 Affects the way the driver calculates the CPU core reference
 140                 voltage from the vid pins.
 141
 142 Also see the Alarms section for status flags associated with voltages.
 143
 144
 145 ********
 146 * Fans *
 147 ********
 148
 149 fan[1-*]_min    Fan minimum value
 150                 Unit: revolution/min (RPM)
 151                 RW
 152
 153 fan[1-*]_max    Fan maximum value
 154                 Unit: revolution/min (RPM)
 155                 Only rarely supported by the hardware.
 156                 RW
 157
 158 fan[1-*]_input  Fan input value.
 159                 Unit: revolution/min (RPM)
 160                 RO
 161
 162 fan[1-*]_div    Fan divisor.
 163                 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
 164                 RW
 165                 Some chips only support values 1, 2, 4 and 8.
 166                 Note that this is actually an internal clock divisor, which
 167                 affects the measurable speed range, not the read value.
 168
 169 fan[1-*]_target
 170                 Desired fan speed
 171                 Unit: revolution/min (RPM)
 172                 RW
 173                 Only makes sense if the chip supports closed-loop fan speed
 174                 control based on the measured fan speed.
 175
 176 fan[1-*]_label  Suggested fan channel label.
 177                 Text string
 178                 Should only be created if the driver has hints about what
 179                 this fan channel is being used for, and user-space doesn't.
 180                 In all other cases, the label is provided by user-space.
 181                 RO
 182
 183 Also see the Alarms section for status flags associated with fans.
 184
 185
 186 *******
 187 * PWM *
 188 *******
 189
 190 pwm[1-*]        Pulse width modulation fan control.
 191                 Integer value in the range 0 to 255
 192                 RW
 193                 255 is max or 100%.
 194
 195 pwm[1-*]_enable
 196                 Fan speed control method:
 197                 0: no fan speed control (i.e. fan at full speed)
 198                 1: manual fan speed control enabled (using pwm[1-*])
 199                 2+: automatic fan speed control enabled
 200                 Check individual chip documentation files for automatic mode
 201                 details.
 202                 RW
 203
 204 pwm[1-*]_mode   0: DC mode (direct current)
 205                 1: PWM mode (pulse-width modulation)
 206                 RW
 207
 208 pwm[1-*]_freq   Base PWM frequency in Hz.
 209                 Only possibly available when pwmN_mode is PWM, but not always
 210                 present even then.
 211                 RW
 212
 213 pwm[1-*]_auto_channels_temp
 214                 Select which temperature channels affect this PWM output in
 215                 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
 216                 Which values are possible depend on the chip used.
 217                 RW
 218
 219 pwm[1-*]_auto_point[1-*]_pwm
 220 pwm[1-*]_auto_point[1-*]_temp
 221 pwm[1-*]_auto_point[1-*]_temp_hyst
 222                 Define the PWM vs temperature curve. Number of trip points is
 223                 chip-dependent. Use this for chips which associate trip points
 224                 to PWM output channels.
 225                 RW
 226
 227 OR
 228
 229 temp[1-*]_auto_point[1-*]_pwm
 230 temp[1-*]_auto_point[1-*]_temp
 231 temp[1-*]_auto_point[1-*]_temp_hyst
 232                 Define the PWM vs temperature curve. Number of trip points is
 233                 chip-dependent. Use this for chips which associate trip points
 234                 to temperature channels.
 235                 RW
 236
 237
 238 ****************
 239 * Temperatures *
 240 ****************
 241
 242 temp[1-*]_type  Sensor type selection.
 243                 Integers 1 to 6
 244                 RW
 245                 1: PII/Celeron Diode
 246                 2: 3904 transistor
 247                 3: thermal diode
 248                 4: thermistor
 249                 5: AMD AMDSI
 250                 6: Intel PECI
 251                 Not all types are supported by all chips
 252
 253 temp[1-*]_max   Temperature max value.
 254                 Unit: millidegree Celsius (or millivolt, see below)
 255                 RW
 256
 257 temp[1-*]_min   Temperature min value.
 258                 Unit: millidegree Celsius
 259                 RW
 260
 261 temp[1-*]_max_hyst
 262                 Temperature hysteresis value for max limit.
 263                 Unit: millidegree Celsius
 264                 Must be reported as an absolute temperature, NOT a delta
 265                 from the max value.
 266                 RW
 267
 268 temp[1-*]_input Temperature input value.
 269                 Unit: millidegree Celsius
 270                 RO
 271
 272 temp[1-*]_crit  Temperature critical value, typically greater than
 273                 corresponding temp_max values.
 274                 Unit: millidegree Celsius
 275                 RW
 276
 277 temp[1-*]_crit_hyst
 278                 Temperature hysteresis value for critical limit.
 279                 Unit: millidegree Celsius
 280                 Must be reported as an absolute temperature, NOT a delta
 281                 from the critical value.
 282                 RW
 283
 284 temp[1-*]_offset
 285                 Temperature offset which is added to the temperature reading
 286                 by the chip.
 287                 Unit: millidegree Celsius
 288                 Read/Write value.
 289
 290 temp[1-*]_label Suggested temperature channel label.
 291                 Text string
 292                 Should only be created if the driver has hints about what
 293                 this temperature channel is being used for, and user-space
 294                 doesn't. In all other cases, the label is provided by
 295                 user-space.
 296                 RO
 297
 298 Some chips measure temperature using external thermistors and an ADC, and
 299 report the temperature measurement as a voltage. Converting this voltage
 300 back to a temperature (or the other way around for limits) requires
 301 mathematical functions not available in the kernel, so the conversion
 302 must occur in user space. For these chips, all temp* files described
 303 above should contain values expressed in millivolt instead of millidegree
 304 Celsius. In other words, such temperature channels are handled as voltage
 305 channels by the driver.
 306
 307 Also see the Alarms section for status flags associated with temperatures.
 308
 309
 310 ************
 311 * Currents *
 312 ************
 313
 314 Note that no known chip provides current measurements as of writing,
 315 so this part is theoretical, so to say.
 316
 317 curr[1-*]_max   Current max value
 318                 Unit: milliampere
 319                 RW
 320
 321 curr[1-*]_min   Current min value.
 322                 Unit: milliampere
 323                 RW
 324
 325 curr[1-*]_input Current input value
 326                 Unit: milliampere
 327                 RO
 328
 329 *********
 330 * Power *
 331 *********
 332
 333 power[1-*]_average              Average power use
 334                                 Unit: microWatt
 335                                 RO
 336
 337 power[1-*]_average_interval     Power use averaging interval
 338                                 Unit: milliseconds
 339                                 RW
 340
 341 power[1-*]_average_highest      Historical average maximum power use
 342                                 Unit: microWatt
 343                                 RO
 344
 345 power[1-*]_average_lowest       Historical average minimum power use
 346                                 Unit: microWatt
 347                                 RO
 348
 349 power[1-*]_input                Instantaneous power use
 350                                 Unit: microWatt
 351                                 RO
 352
 353 power[1-*]_input_highest        Historical maximum power use
 354                                 Unit: microWatt
 355                                 RO
 356
 357 power[1-*]_input_lowest         Historical minimum power use
 358                                 Unit: microWatt
 359                                 RO
 360
 361 power[1-*]_reset_history        Reset input_highest, input_lowest,
 362                                 average_highest and average_lowest.
 363                                 WO
 364
 365 **********
 366 * Energy *
 367 **********
 368
 369 energy[1-*]_input               Cumulative energy use
 370                                 Unit: microJoule
 371                                 RO
 372
 373
 374 **********
 375 * Alarms *
 376 **********
 377
 378 Each channel or limit may have an associated alarm file, containing a
 379 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
 380
 381 Usually a given chip will either use channel-related alarms, or
 382 limit-related alarms, not both. The driver should just reflect the hardware
 383 implementation.
 384
 385 in[0-*]_alarm
 386 fan[1-*]_alarm
 387 temp[1-*]_alarm
 388                 Channel alarm
 389                 0: no alarm
 390                 1: alarm
 391                 RO
 392
 393 OR
 394
 395 in[0-*]_min_alarm
 396 in[0-*]_max_alarm
 397 fan[1-*]_min_alarm
 398 fan[1-*]_max_alarm
 399 temp[1-*]_min_alarm
 400 temp[1-*]_max_alarm
 401 temp[1-*]_crit_alarm
 402                 Limit alarm
 403                 0: no alarm
 404                 1: alarm
 405                 RO
 406
 407 Each input channel may have an associated fault file. This can be used
 408 to notify open diodes, unconnected fans etc. where the hardware
 409 supports it. When this boolean has value 1, the measurement for that
 410 channel should not be trusted.
 411
 412 in[0-*]_fault
 413 fan[1-*]_fault
 414 temp[1-*]_fault
 415                 Input fault condition
 416                 0: no fault occured
 417                 1: fault condition
 418                 RO
 419
 420 Some chips also offer the possibility to get beeped when an alarm occurs:
 421
 422 beep_enable     Master beep enable
 423                 0: no beeps
 424                 1: beeps
 425                 RW
 426
 427 in[0-*]_beep
 428 fan[1-*]_beep
 429 temp[1-*]_beep
 430                 Channel beep
 431                 0: disable
 432                 1: enable
 433                 RW
 434
 435 In theory, a chip could provide per-limit beep masking, but no such chip
 436 was seen so far.
 437
 438 Old drivers provided a different, non-standard interface to alarms and
 439 beeps. These interface files are deprecated, but will be kept around
 440 for compatibility reasons:
 441
 442 alarms          Alarm bitmask.
 443                 RO
 444                 Integer representation of one to four bytes.
 445                 A '1' bit means an alarm.
 446                 Chips should be programmed for 'comparator' mode so that
 447                 the alarm will 'come back' after you read the register
 448                 if it is still valid.
 449                 Generally a direct representation of a chip's internal
 450                 alarm registers; there is no standard for the position
 451                 of individual bits. For this reason, the use of this
 452                 interface file for new drivers is discouraged. Use
 453                 individual *_alarm and *_fault files instead.
 454                 Bits are defined in kernel/include/sensors.h.
 455
 456 beep_mask       Bitmask for beep.
 457                 Same format as 'alarms' with the same bit locations,
 458                 use discouraged for the same reason. Use individual
 459                 *_beep files instead.
 460                 RW
 461
 462
 463 ***********************
 464 * Intrusion detection *
 465 ***********************
 466
 467 intrusion[0-*]_alarm
 468                 Chassis intrusion detection
 469                 0: OK
 470                 1: intrusion detected
 471                 RW
 472                 Contrary to regular alarm flags which clear themselves
 473                 automatically when read, this one sticks until cleared by
 474                 the user. This is done by writing 0 to the file. Writing
 475                 other values is unsupported.
 476
 477 intrusion[0-*]_beep
 478                 Chassis intrusion beep
 479                 0: disable
 480                 1: enable
 481                 RW
 482
 483
 484 sysfs attribute writes interpretation
 485 -------------------------------------
 486
 487 hwmon sysfs attributes always contain numbers, so the first thing to do is to
 488 convert the input to a number, there are 2 ways todo this depending whether
 489 the number can be negative or not:
 490 unsigned long u = simple_strtoul(buf, NULL, 10);
 491 long s = simple_strtol(buf, NULL, 10);
 492
 493 With buf being the buffer with the user input being passed by the kernel.
 494 Notice that we do not use the second argument of strto[u]l, and thus cannot
 495 tell when 0 is returned, if this was really 0 or is caused by invalid input.
 496 This is done deliberately as checking this everywhere would add a lot of
 497 code to the kernel.
 498
 499 Notice that it is important to always store the converted value in an
 500 unsigned long or long, so that no wrap around can happen before any further
 501 checking.
 502
 503 After the input string is converted to an (unsigned) long, the value should be
 504 checked if its acceptable. Be careful with further conversions on the value
 505 before checking it for validity, as these conversions could still cause a wrap
 506 around before the check. For example do not multiply the result, and only
 507 add/subtract if it has been divided before the add/subtract.
 508
 509 What to do if a value is found to be invalid, depends on the type of the
 510 sysfs attribute that is being set. If it is a continuous setting like a
 511 tempX_max or inX_max attribute, then the value should be clamped to its
 512 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
 513 continuous like for example a tempX_type, then when an invalid value is
 514 written, -EINVAL should be returned.
 515
 516 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
 517
 518         long v = simple_strtol(buf, NULL, 10) / 1000;
 519         v = SENSORS_LIMIT(v, -128, 127);
 520         /* write v to register */
 521
 522 Example2, fan divider setting, valid values 2, 4 and 8:
 523
 524         unsigned long v = simple_strtoul(buf, NULL, 10);
 525
 526         switch (v) {
 527         case 2: v = 1; break;
 528         case 4: v = 2; break;
 529         case 8: v = 3; break;
 530         default:
 531                 return -EINVAL;
 532         }
 533         /* write v to register */