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 WO      write only value
  74 RW      read/write value
  75
  76 Read/write values may be read-only for some chips, depending on the
  77 hardware implementation.
  78
  79 All entries (except name) are optional, and should only be created in a
  80 given driver if the chip has the feature.
  81
  82
  83 *********************
  84 * Global attributes *
  85 *********************
  86
  87 name            The chip name.
  88                 This should be a short, lowercase string, not containing
  89                 spaces nor dashes, representing the chip name. This is
  90                 the only mandatory attribute.
  91                 I2C devices get this attribute created automatically.
  92                 RO
  93
  94 update_rate     The rate at which the chip will update readings.
  95                 Unit: millisecond
  96                 RW
  97                 Some devices have a variable update rate. This attribute
  98                 can be used to change the update rate to the desired
  99                 frequency.
 100
 101
 102 ************
 103 * Voltages *
 104 ************
 105
 106 in[0-*]_min     Voltage min value.
 107                 Unit: millivolt
 108                 RW
 109
 110 in[0-*]_lcrit   Voltage critical min value.
 111                 Unit: millivolt
 112                 RW
 113                 If voltage drops to or below this limit, the system may
 114                 take drastic action such as power down or reset. At the very
 115                 least, it should report a fault.
 116
 117 in[0-*]_max     Voltage max value.
 118                 Unit: millivolt
 119                 RW
 120
 121 in[0-*]_crit    Voltage critical max value.
 122                 Unit: millivolt
 123                 RW
 124                 If voltage reaches or exceeds this limit, the system may
 125                 take drastic action such as power down or reset. At the very
 126                 least, it should report a fault.
 127
 128 in[0-*]_input   Voltage input value.
 129                 Unit: millivolt
 130                 RO
 131                 Voltage measured on the chip pin.
 132                 Actual voltage depends on the scaling resistors on the
 133                 motherboard, as recommended in the chip datasheet.
 134                 This varies by chip and by motherboard.
 135                 Because of this variation, values are generally NOT scaled
 136                 by the chip driver, and must be done by the application.
 137                 However, some drivers (notably lm87 and via686a)
 138                 do scale, because of internal resistors built into a chip.
 139                 These drivers will output the actual voltage. Rule of
 140                 thumb: drivers should report the voltage values at the
 141                 "pins" of the chip.
 142
 143 in[0-*]_label   Suggested voltage channel label.
 144                 Text string
 145                 Should only be created if the driver has hints about what
 146                 this voltage channel is being used for, and user-space
 147                 doesn't. In all other cases, the label is provided by
 148                 user-space.
 149                 RO
 150
 151 cpu[0-*]_vid    CPU core reference voltage.
 152                 Unit: millivolt
 153                 RO
 154                 Not always correct.
 155
 156 vrm             Voltage Regulator Module version number.
 157                 RW (but changing it should no more be necessary)
 158                 Originally the VRM standard version multiplied by 10, but now
 159                 an arbitrary number, as not all standards have a version
 160                 number.
 161                 Affects the way the driver calculates the CPU core reference
 162                 voltage from the vid pins.
 163
 164 Also see the Alarms section for status flags associated with voltages.
 165
 166
 167 ********
 168 * Fans *
 169 ********
 170
 171 fan[1-*]_min    Fan minimum value
 172                 Unit: revolution/min (RPM)
 173                 RW
 174
 175 fan[1-*]_max    Fan maximum value
 176                 Unit: revolution/min (RPM)
 177                 Only rarely supported by the hardware.
 178                 RW
 179
 180 fan[1-*]_input  Fan input value.
 181                 Unit: revolution/min (RPM)
 182                 RO
 183
 184 fan[1-*]_div    Fan divisor.
 185                 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
 186                 RW
 187                 Some chips only support values 1, 2, 4 and 8.
 188                 Note that this is actually an internal clock divisor, which
 189                 affects the measurable speed range, not the read value.
 190
 191 fan[1-*]_target
 192                 Desired fan speed
 193                 Unit: revolution/min (RPM)
 194                 RW
 195                 Only makes sense if the chip supports closed-loop fan speed
 196                 control based on the measured fan speed.
 197
 198 fan[1-*]_label  Suggested fan channel label.
 199                 Text string
 200                 Should only be created if the driver has hints about what
 201                 this fan channel is being used for, and user-space doesn't.
 202                 In all other cases, the label is provided by user-space.
 203                 RO
 204
 205 Also see the Alarms section for status flags associated with fans.
 206
 207
 208 *******
 209 * PWM *
 210 *******
 211
 212 pwm[1-*]        Pulse width modulation fan control.
 213                 Integer value in the range 0 to 255
 214                 RW
 215                 255 is max or 100%.
 216
 217 pwm[1-*]_enable
 218                 Fan speed control method:
 219                 0: no fan speed control (i.e. fan at full speed)
 220                 1: manual fan speed control enabled (using pwm[1-*])
 221                 2+: automatic fan speed control enabled
 222                 Check individual chip documentation files for automatic mode
 223                 details.
 224                 RW
 225
 226 pwm[1-*]_mode   0: DC mode (direct current)
 227                 1: PWM mode (pulse-width modulation)
 228                 RW
 229
 230 pwm[1-*]_freq   Base PWM frequency in Hz.
 231                 Only possibly available when pwmN_mode is PWM, but not always
 232                 present even then.
 233                 RW
 234
 235 pwm[1-*]_auto_channels_temp
 236                 Select which temperature channels affect this PWM output in
 237                 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
 238                 Which values are possible depend on the chip used.
 239                 RW
 240
 241 pwm[1-*]_auto_point[1-*]_pwm
 242 pwm[1-*]_auto_point[1-*]_temp
 243 pwm[1-*]_auto_point[1-*]_temp_hyst
 244                 Define the PWM vs temperature curve. Number of trip points is
 245                 chip-dependent. Use this for chips which associate trip points
 246                 to PWM output channels.
 247                 RW
 248
 249 temp[1-*]_auto_point[1-*]_pwm
 250 temp[1-*]_auto_point[1-*]_temp
 251 temp[1-*]_auto_point[1-*]_temp_hyst
 252                 Define the PWM vs temperature curve. Number of trip points is
 253                 chip-dependent. Use this for chips which associate trip points
 254                 to temperature channels.
 255                 RW
 256
 257 There is a third case where trip points are associated to both PWM output
 258 channels and temperature channels: the PWM values are associated to PWM
 259 output channels while the temperature values are associated to temperature
 260 channels. In that case, the result is determined by the mapping between
 261 temperature inputs and PWM outputs. When several temperature inputs are
 262 mapped to a given PWM output, this leads to several candidate PWM values.
 263 The actual result is up to the chip, but in general the highest candidate
 264 value (fastest fan speed) wins.
 265
 266
 267 ****************
 268 * Temperatures *
 269 ****************
 270
 271 temp[1-*]_type  Sensor type selection.
 272                 Integers 1 to 6
 273                 RW
 274                 1: PII/Celeron Diode
 275                 2: 3904 transistor
 276                 3: thermal diode
 277                 4: thermistor
 278                 5: AMD AMDSI
 279                 6: Intel PECI
 280                 Not all types are supported by all chips
 281
 282 temp[1-*]_max   Temperature max value.
 283                 Unit: millidegree Celsius (or millivolt, see below)
 284                 RW
 285
 286 temp[1-*]_min   Temperature min value.
 287                 Unit: millidegree Celsius
 288                 RW
 289
 290 temp[1-*]_max_hyst
 291                 Temperature hysteresis value for max limit.
 292                 Unit: millidegree Celsius
 293                 Must be reported as an absolute temperature, NOT a delta
 294                 from the max value.
 295                 RW
 296
 297 temp[1-*]_input Temperature input value.
 298                 Unit: millidegree Celsius
 299                 RO
 300
 301 temp[1-*]_crit  Temperature critical max value, typically greater than
 302                 corresponding temp_max values.
 303                 Unit: millidegree Celsius
 304                 RW
 305
 306 temp[1-*]_crit_hyst
 307                 Temperature hysteresis value for critical limit.
 308                 Unit: millidegree Celsius
 309                 Must be reported as an absolute temperature, NOT a delta
 310                 from the critical value.
 311                 RW
 312
 313 temp[1-*]_lcrit Temperature critical min value, typically lower than
 314                 corresponding temp_min values.
 315                 Unit: millidegree Celsius
 316                 RW
 317
 318 temp[1-*]_offset
 319                 Temperature offset which is added to the temperature reading
 320                 by the chip.
 321                 Unit: millidegree Celsius
 322                 Read/Write value.
 323
 324 temp[1-*]_label Suggested temperature channel label.
 325                 Text string
 326                 Should only be created if the driver has hints about what
 327                 this temperature channel is being used for, and user-space
 328                 doesn't. In all other cases, the label is provided by
 329                 user-space.
 330                 RO
 331
 332 temp[1-*]_lowest
 333                 Historical minimum temperature
 334                 Unit: millidegree Celsius
 335                 RO
 336
 337 temp[1-*]_highest
 338                 Historical maximum temperature
 339                 Unit: millidegree Celsius
 340                 RO
 341
 342 temp[1-*]_reset_history
 343                 Reset temp_lowest and temp_highest
 344                 WO
 345
 346 temp_reset_history
 347                 Reset temp_lowest and temp_highest for all sensors
 348                 WO
 349
 350 Some chips measure temperature using external thermistors and an ADC, and
 351 report the temperature measurement as a voltage. Converting this voltage
 352 back to a temperature (or the other way around for limits) requires
 353 mathematical functions not available in the kernel, so the conversion
 354 must occur in user space. For these chips, all temp* files described
 355 above should contain values expressed in millivolt instead of millidegree
 356 Celsius. In other words, such temperature channels are handled as voltage
 357 channels by the driver.
 358
 359 Also see the Alarms section for status flags associated with temperatures.
 360
 361
 362 ************
 363 * Currents *
 364 ************
 365
 366 curr[1-*]_max   Current max value
 367                 Unit: milliampere
 368                 RW
 369
 370 curr[1-*]_min   Current min value.
 371                 Unit: milliampere
 372                 RW
 373
 374 curr[1-*]_input Current input value
 375                 Unit: milliampere
 376                 RO
 377
 378 *********
 379 * Power *
 380 *********
 381
 382 power[1-*]_average              Average power use
 383                                 Unit: microWatt
 384                                 RO
 385
 386 power[1-*]_average_interval     Power use averaging interval.  A poll
 387                                 notification is sent to this file if the
 388                                 hardware changes the averaging interval.
 389                                 Unit: milliseconds
 390                                 RW
 391
 392 power[1-*]_average_interval_max Maximum power use averaging interval
 393                                 Unit: milliseconds
 394                                 RO
 395
 396 power[1-*]_average_interval_min Minimum power use averaging interval
 397                                 Unit: milliseconds
 398                                 RO
 399
 400 power[1-*]_average_highest      Historical average maximum power use
 401                                 Unit: microWatt
 402                                 RO
 403
 404 power[1-*]_average_lowest       Historical average minimum power use
 405                                 Unit: microWatt
 406                                 RO
 407
 408 power[1-*]_average_max          A poll notification is sent to
 409                                 power[1-*]_average when power use
 410                                 rises above this value.
 411                                 Unit: microWatt
 412                                 RW
 413
 414 power[1-*]_average_min          A poll notification is sent to
 415                                 power[1-*]_average when power use
 416                                 sinks below this value.
 417                                 Unit: microWatt
 418                                 RW
 419
 420 power[1-*]_input                Instantaneous power use
 421                                 Unit: microWatt
 422                                 RO
 423
 424 power[1-*]_input_highest        Historical maximum power use
 425                                 Unit: microWatt
 426                                 RO
 427
 428 power[1-*]_input_lowest         Historical minimum power use
 429                                 Unit: microWatt
 430                                 RO
 431
 432 power[1-*]_reset_history        Reset input_highest, input_lowest,
 433                                 average_highest and average_lowest.
 434                                 WO
 435
 436 power[1-*]_accuracy             Accuracy of the power meter.
 437                                 Unit: Percent
 438                                 RO
 439
 440 power[1-*]_alarm                1 if the system is drawing more power than the
 441                                 cap allows; 0 otherwise.  A poll notification is
 442                                 sent to this file when the power use exceeds the
 443                                 cap.  This file only appears if the cap is known
 444                                 to be enforced by hardware.
 445                                 RO
 446
 447 power[1-*]_cap                  If power use rises above this limit, the
 448                                 system should take action to reduce power use.
 449                                 A poll notification is sent to this file if the
 450                                 cap is changed by the hardware.  The *_cap
 451                                 files only appear if the cap is known to be
 452                                 enforced by hardware.
 453                                 Unit: microWatt
 454                                 RW
 455
 456 power[1-*]_cap_hyst             Margin of hysteresis built around capping and
 457                                 notification.
 458                                 Unit: microWatt
 459                                 RW
 460
 461 power[1-*]_cap_max              Maximum cap that can be set.
 462                                 Unit: microWatt
 463                                 RO
 464
 465 power[1-*]_cap_min              Minimum cap that can be set.
 466                                 Unit: microWatt
 467                                 RO
 468
 469 **********
 470 * Energy *
 471 **********
 472
 473 energy[1-*]_input               Cumulative energy use
 474                                 Unit: microJoule
 475                                 RO
 476
 477
 478 **********
 479 * Alarms *
 480 **********
 481
 482 Each channel or limit may have an associated alarm file, containing a
 483 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
 484
 485 Usually a given chip will either use channel-related alarms, or
 486 limit-related alarms, not both. The driver should just reflect the hardware
 487 implementation.
 488
 489 in[0-*]_alarm
 490 curr[1-*]_alarm
 491 fan[1-*]_alarm
 492 temp[1-*]_alarm
 493                 Channel alarm
 494                 0: no alarm
 495                 1: alarm
 496                 RO
 497
 498 OR
 499
 500 in[0-*]_min_alarm
 501 in[0-*]_max_alarm
 502 curr[1-*]_min_alarm
 503 curr[1-*]_max_alarm
 504 fan[1-*]_min_alarm
 505 fan[1-*]_max_alarm
 506 temp[1-*]_min_alarm
 507 temp[1-*]_max_alarm
 508 temp[1-*]_crit_alarm
 509                 Limit alarm
 510                 0: no alarm
 511                 1: alarm
 512                 RO
 513
 514 Each input channel may have an associated fault file. This can be used
 515 to notify open diodes, unconnected fans etc. where the hardware
 516 supports it. When this boolean has value 1, the measurement for that
 517 channel should not be trusted.
 518
 519 fan[1-*]_fault
 520 temp[1-*]_fault
 521                 Input fault condition
 522                 0: no fault occured
 523                 1: fault condition
 524                 RO
 525
 526 Some chips also offer the possibility to get beeped when an alarm occurs:
 527
 528 beep_enable     Master beep enable
 529                 0: no beeps
 530                 1: beeps
 531                 RW
 532
 533 in[0-*]_beep
 534 curr[1-*]_beep
 535 fan[1-*]_beep
 536 temp[1-*]_beep
 537                 Channel beep
 538                 0: disable
 539                 1: enable
 540                 RW
 541
 542 In theory, a chip could provide per-limit beep masking, but no such chip
 543 was seen so far.
 544
 545 Old drivers provided a different, non-standard interface to alarms and
 546 beeps. These interface files are deprecated, but will be kept around
 547 for compatibility reasons:
 548
 549 alarms          Alarm bitmask.
 550                 RO
 551                 Integer representation of one to four bytes.
 552                 A '1' bit means an alarm.
 553                 Chips should be programmed for 'comparator' mode so that
 554                 the alarm will 'come back' after you read the register
 555                 if it is still valid.
 556                 Generally a direct representation of a chip's internal
 557                 alarm registers; there is no standard for the position
 558                 of individual bits. For this reason, the use of this
 559                 interface file for new drivers is discouraged. Use
 560                 individual *_alarm and *_fault files instead.
 561                 Bits are defined in kernel/include/sensors.h.
 562
 563 beep_mask       Bitmask for beep.
 564                 Same format as 'alarms' with the same bit locations,
 565                 use discouraged for the same reason. Use individual
 566                 *_beep files instead.
 567                 RW
 568
 569
 570 ***********************
 571 * Intrusion detection *
 572 ***********************
 573
 574 intrusion[0-*]_alarm
 575                 Chassis intrusion detection
 576                 0: OK
 577                 1: intrusion detected
 578                 RW
 579                 Contrary to regular alarm flags which clear themselves
 580                 automatically when read, this one sticks until cleared by
 581                 the user. This is done by writing 0 to the file. Writing
 582                 other values is unsupported.
 583
 584 intrusion[0-*]_beep
 585                 Chassis intrusion beep
 586                 0: disable
 587                 1: enable
 588                 RW
 589
 590
 591 sysfs attribute writes interpretation
 592 -------------------------------------
 593
 594 hwmon sysfs attributes always contain numbers, so the first thing to do is to
 595 convert the input to a number, there are 2 ways todo this depending whether
 596 the number can be negative or not:
 597 unsigned long u = simple_strtoul(buf, NULL, 10);
 598 long s = simple_strtol(buf, NULL, 10);
 599
 600 With buf being the buffer with the user input being passed by the kernel.
 601 Notice that we do not use the second argument of strto[u]l, and thus cannot
 602 tell when 0 is returned, if this was really 0 or is caused by invalid input.
 603 This is done deliberately as checking this everywhere would add a lot of
 604 code to the kernel.
 605
 606 Notice that it is important to always store the converted value in an
 607 unsigned long or long, so that no wrap around can happen before any further
 608 checking.
 609
 610 After the input string is converted to an (unsigned) long, the value should be
 611 checked if its acceptable. Be careful with further conversions on the value
 612 before checking it for validity, as these conversions could still cause a wrap
 613 around before the check. For example do not multiply the result, and only
 614 add/subtract if it has been divided before the add/subtract.
 615
 616 What to do if a value is found to be invalid, depends on the type of the
 617 sysfs attribute that is being set. If it is a continuous setting like a
 618 tempX_max or inX_max attribute, then the value should be clamped to its
 619 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
 620 continuous like for example a tempX_type, then when an invalid value is
 621 written, -EINVAL should be returned.
 622
 623 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
 624
 625         long v = simple_strtol(buf, NULL, 10) / 1000;
 626         v = SENSORS_LIMIT(v, -128, 127);
 627         /* write v to register */
 628
 629 Example2, fan divider setting, valid values 2, 4 and 8:
 630
 631         unsigned long v = simple_strtoul(buf, NULL, 10);
 632
 633         switch (v) {
 634         case 2: v = 1; break;
 635         case 4: v = 2; break;
 636         case 8: v = 3; break;
 637         default:
 638                 return -EINVAL;
 639         }
 640         /* write v to register */