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-*]_input  Fan input value.
 154                 Unit: revolution/min (RPM)
 155                 RO
 156
 157 fan[1-*]_div    Fan divisor.
 158                 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
 159                 RW
 160                 Some chips only support values 1, 2, 4 and 8.
 161                 Note that this is actually an internal clock divisor, which
 162                 affects the measurable speed range, not the read value.
 163
 164 fan[1-*]_target
 165                 Desired fan speed
 166                 Unit: revolution/min (RPM)
 167                 RW
 168                 Only makes sense if the chip supports closed-loop fan speed
 169                 control based on the measured fan speed.
 170
 171 fan[1-*]_label  Suggested fan channel label.
 172                 Text string
 173                 Should only be created if the driver has hints about what
 174                 this fan channel is being used for, and user-space doesn't.
 175                 In all other cases, the label is provided by user-space.
 176                 RO
 177
 178 Also see the Alarms section for status flags associated with fans.
 179
 180
 181 *******
 182 * PWM *
 183 *******
 184
 185 pwm[1-*]        Pulse width modulation fan control.
 186                 Integer value in the range 0 to 255
 187                 RW
 188                 255 is max or 100%.
 189
 190 pwm[1-*]_enable
 191                 Fan speed control method:
 192                 0: no fan speed control (i.e. fan at full speed)
 193                 1: manual fan speed control enabled (using pwm[1-*])
 194                 2+: automatic fan speed control enabled
 195                 Check individual chip documentation files for automatic mode
 196                 details.
 197                 RW
 198
 199 pwm[1-*]_mode   0: DC mode (direct current)
 200                 1: PWM mode (pulse-width modulation)
 201                 RW
 202
 203 pwm[1-*]_freq   Base PWM frequency in Hz.
 204                 Only possibly available when pwmN_mode is PWM, but not always
 205                 present even then.
 206                 RW
 207
 208 pwm[1-*]_auto_channels_temp
 209                 Select which temperature channels affect this PWM output in
 210                 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
 211                 Which values are possible depend on the chip used.
 212                 RW
 213
 214 pwm[1-*]_auto_point[1-*]_pwm
 215 pwm[1-*]_auto_point[1-*]_temp
 216 pwm[1-*]_auto_point[1-*]_temp_hyst
 217                 Define the PWM vs temperature curve. Number of trip points is
 218                 chip-dependent. Use this for chips which associate trip points
 219                 to PWM output channels.
 220                 RW
 221
 222 OR
 223
 224 temp[1-*]_auto_point[1-*]_pwm
 225 temp[1-*]_auto_point[1-*]_temp
 226 temp[1-*]_auto_point[1-*]_temp_hyst
 227                 Define the PWM vs temperature curve. Number of trip points is
 228                 chip-dependent. Use this for chips which associate trip points
 229                 to temperature channels.
 230                 RW
 231
 232
 233 ****************
 234 * Temperatures *
 235 ****************
 236
 237 temp[1-*]_type  Sensor type selection.
 238                 Integers 1 to 6
 239                 RW
 240                 1: PII/Celeron Diode
 241                 2: 3904 transistor
 242                 3: thermal diode
 243                 4: thermistor
 244                 5: AMD AMDSI
 245                 6: Intel PECI
 246                 Not all types are supported by all chips
 247
 248 temp[1-*]_max   Temperature max value.
 249                 Unit: millidegree Celsius (or millivolt, see below)
 250                 RW
 251
 252 temp[1-*]_min   Temperature min value.
 253                 Unit: millidegree Celsius
 254                 RW
 255
 256 temp[1-*]_max_hyst
 257                 Temperature hysteresis value for max limit.
 258                 Unit: millidegree Celsius
 259                 Must be reported as an absolute temperature, NOT a delta
 260                 from the max value.
 261                 RW
 262
 263 temp[1-*]_input Temperature input value.
 264                 Unit: millidegree Celsius
 265                 RO
 266
 267 temp[1-*]_crit  Temperature critical value, typically greater than
 268                 corresponding temp_max values.
 269                 Unit: millidegree Celsius
 270                 RW
 271
 272 temp[1-*]_crit_hyst
 273                 Temperature hysteresis value for critical limit.
 274                 Unit: millidegree Celsius
 275                 Must be reported as an absolute temperature, NOT a delta
 276                 from the critical value.
 277                 RW
 278
 279 temp[1-*]_offset
 280                 Temperature offset which is added to the temperature reading
 281                 by the chip.
 282                 Unit: millidegree Celsius
 283                 Read/Write value.
 284
 285 temp[1-*]_label Suggested temperature channel label.
 286                 Text string
 287                 Should only be created if the driver has hints about what
 288                 this temperature channel is being used for, and user-space
 289                 doesn't. In all other cases, the label is provided by
 290                 user-space.
 291                 RO
 292
 293 Some chips measure temperature using external thermistors and an ADC, and
 294 report the temperature measurement as a voltage. Converting this voltage
 295 back to a temperature (or the other way around for limits) requires
 296 mathematical functions not available in the kernel, so the conversion
 297 must occur in user space. For these chips, all temp* files described
 298 above should contain values expressed in millivolt instead of millidegree
 299 Celsius. In other words, such temperature channels are handled as voltage
 300 channels by the driver.
 301
 302 Also see the Alarms section for status flags associated with temperatures.
 303
 304
 305 ************
 306 * Currents *
 307 ************
 308
 309 Note that no known chip provides current measurements as of writing,
 310 so this part is theoretical, so to say.
 311
 312 curr[1-*]_max   Current max value
 313                 Unit: milliampere
 314                 RW
 315
 316 curr[1-*]_min   Current min value.
 317                 Unit: milliampere
 318                 RW
 319
 320 curr[1-*]_input Current input value
 321                 Unit: milliampere
 322                 RO
 323
 324 *********
 325 * Power *
 326 *********
 327
 328 power[1-*]_average              Average power use
 329                                 Unit: microWatt
 330                                 RO
 331
 332 power[1-*]_average_highest      Historical average maximum power use
 333                                 Unit: microWatt
 334                                 RO
 335
 336 power[1-*]_average_lowest       Historical average minimum power use
 337                                 Unit: microWatt
 338                                 RO
 339
 340 power[1-*]_input                Instantaneous power use
 341                                 Unit: microWatt
 342                                 RO
 343
 344 power[1-*]_input_highest        Historical maximum power use
 345                                 Unit: microWatt
 346                                 RO
 347
 348 power[1-*]_input_lowest         Historical minimum power use
 349                                 Unit: microWatt
 350                                 RO
 351
 352 power[1-*]_reset_history        Reset input_highest, input_lowest,
 353                                 average_highest and average_lowest.
 354                                 WO
 355
 356 **********
 357 * Alarms *
 358 **********
 359
 360 Each channel or limit may have an associated alarm file, containing a
 361 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
 362
 363 Usually a given chip will either use channel-related alarms, or
 364 limit-related alarms, not both. The driver should just reflect the hardware
 365 implementation.
 366
 367 in[0-*]_alarm
 368 fan[1-*]_alarm
 369 temp[1-*]_alarm
 370                 Channel alarm
 371                 0: no alarm
 372                 1: alarm
 373                 RO
 374
 375 OR
 376
 377 in[0-*]_min_alarm
 378 in[0-*]_max_alarm
 379 fan[1-*]_min_alarm
 380 temp[1-*]_min_alarm
 381 temp[1-*]_max_alarm
 382 temp[1-*]_crit_alarm
 383                 Limit alarm
 384                 0: no alarm
 385                 1: alarm
 386                 RO
 387
 388 Each input channel may have an associated fault file. This can be used
 389 to notify open diodes, unconnected fans etc. where the hardware
 390 supports it. When this boolean has value 1, the measurement for that
 391 channel should not be trusted.
 392
 393 in[0-*]_fault
 394 fan[1-*]_fault
 395 temp[1-*]_fault
 396                 Input fault condition
 397                 0: no fault occured
 398                 1: fault condition
 399                 RO
 400
 401 Some chips also offer the possibility to get beeped when an alarm occurs:
 402
 403 beep_enable     Master beep enable
 404                 0: no beeps
 405                 1: beeps
 406                 RW
 407
 408 in[0-*]_beep
 409 fan[1-*]_beep
 410 temp[1-*]_beep
 411                 Channel beep
 412                 0: disable
 413                 1: enable
 414                 RW
 415
 416 In theory, a chip could provide per-limit beep masking, but no such chip
 417 was seen so far.
 418
 419 Old drivers provided a different, non-standard interface to alarms and
 420 beeps. These interface files are deprecated, but will be kept around
 421 for compatibility reasons:
 422
 423 alarms          Alarm bitmask.
 424                 RO
 425                 Integer representation of one to four bytes.
 426                 A '1' bit means an alarm.
 427                 Chips should be programmed for 'comparator' mode so that
 428                 the alarm will 'come back' after you read the register
 429                 if it is still valid.
 430                 Generally a direct representation of a chip's internal
 431                 alarm registers; there is no standard for the position
 432                 of individual bits. For this reason, the use of this
 433                 interface file for new drivers is discouraged. Use
 434                 individual *_alarm and *_fault files instead.
 435                 Bits are defined in kernel/include/sensors.h.
 436
 437 beep_mask       Bitmask for beep.
 438                 Same format as 'alarms' with the same bit locations,
 439                 use discouraged for the same reason. Use individual
 440                 *_beep files instead.
 441                 RW
 442
 443
 444 sysfs attribute writes interpretation
 445 -------------------------------------
 446
 447 hwmon sysfs attributes always contain numbers, so the first thing to do is to
 448 convert the input to a number, there are 2 ways todo this depending whether
 449 the number can be negative or not:
 450 unsigned long u = simple_strtoul(buf, NULL, 10);
 451 long s = simple_strtol(buf, NULL, 10);
 452
 453 With buf being the buffer with the user input being passed by the kernel.
 454 Notice that we do not use the second argument of strto[u]l, and thus cannot
 455 tell when 0 is returned, if this was really 0 or is caused by invalid input.
 456 This is done deliberately as checking this everywhere would add a lot of
 457 code to the kernel.
 458
 459 Notice that it is important to always store the converted value in an
 460 unsigned long or long, so that no wrap around can happen before any further
 461 checking.
 462
 463 After the input string is converted to an (unsigned) long, the value should be
 464 checked if its acceptable. Be careful with further conversions on the value
 465 before checking it for validity, as these conversions could still cause a wrap
 466 around before the check. For example do not multiply the result, and only
 467 add/subtract if it has been divided before the add/subtract.
 468
 469 What to do if a value is found to be invalid, depends on the type of the
 470 sysfs attribute that is being set. If it is a continuous setting like a
 471 tempX_max or inX_max attribute, then the value should be clamped to its
 472 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
 473 continuous like for example a tempX_type, then when an invalid value is
 474 written, -EINVAL should be returned.
 475
 476 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
 477
 478         long v = simple_strtol(buf, NULL, 10) / 1000;
 479         v = SENSORS_LIMIT(v, -128, 127);
 480         /* write v to register */
 481
 482 Example2, fan divider setting, valid values 2, 4 and 8:
 483
 484         unsigned long v = simple_strtoul(buf, NULL, 10);
 485
 486         switch (v) {
 487         case 2: v = 1; break;
 488         case 4: v = 2; break;
 489         case 8: v = 3; break;
 490         default:
 491                 return -EINVAL;
 492         }
 493         /* write v to register */