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_interval The interval at which the chip will update readings.
  95                 Unit: millisecond
  96                 RW
  97                 Some devices have a variable update rate or interval.
  98                 This attribute can be used to change it to the desired value.
  99
 100
 101 ************
 102 * Voltages *
 103 ************
 104
 105 in[0-*]_min     Voltage min value.
 106                 Unit: millivolt
 107                 RW
 108
 109 in[0-*]_lcrit   Voltage critical min value.
 110                 Unit: millivolt
 111                 RW
 112                 If voltage drops to or below this limit, the system may
 113                 take drastic action such as power down or reset. At the very
 114                 least, it should report a fault.
 115
 116 in[0-*]_max     Voltage max value.
 117                 Unit: millivolt
 118                 RW
 119
 120 in[0-*]_crit    Voltage critical max value.
 121                 Unit: millivolt
 122                 RW
 123                 If voltage reaches or exceeds this limit, the system may
 124                 take drastic action such as power down or reset. At the very
 125                 least, it should report a fault.
 126
 127 in[0-*]_input   Voltage input value.
 128                 Unit: millivolt
 129                 RO
 130                 Voltage measured on the chip pin.
 131                 Actual voltage depends on the scaling resistors on the
 132                 motherboard, as recommended in the chip datasheet.
 133                 This varies by chip and by motherboard.
 134                 Because of this variation, values are generally NOT scaled
 135                 by the chip driver, and must be done by the application.
 136                 However, some drivers (notably lm87 and via686a)
 137                 do scale, because of internal resistors built into a chip.
 138                 These drivers will output the actual voltage. Rule of
 139                 thumb: drivers should report the voltage values at the
 140                 "pins" of the chip.
 141
 142 in[0-*]_average
 143                 Average voltage
 144                 Unit: millivolt
 145                 RO
 146
 147 in[0-*]_lowest
 148                 Historical minimum voltage
 149                 Unit: millivolt
 150                 RO
 151
 152 in[0-*]_highest
 153                 Historical maximum voltage
 154                 Unit: millivolt
 155                 RO
 156
 157 in[0-*]_reset_history
 158                 Reset inX_lowest and inX_highest
 159                 WO
 160
 161 in_reset_history
 162                 Reset inX_lowest and inX_highest for all sensors
 163                 WO
 164
 165 in[0-*]_label   Suggested voltage channel label.
 166                 Text string
 167                 Should only be created if the driver has hints about what
 168                 this voltage channel is being used for, and user-space
 169                 doesn't. In all other cases, the label is provided by
 170                 user-space.
 171                 RO
 172
 173 cpu[0-*]_vid    CPU core reference voltage.
 174                 Unit: millivolt
 175                 RO
 176                 Not always correct.
 177
 178 vrm             Voltage Regulator Module version number.
 179                 RW (but changing it should no more be necessary)
 180                 Originally the VRM standard version multiplied by 10, but now
 181                 an arbitrary number, as not all standards have a version
 182                 number.
 183                 Affects the way the driver calculates the CPU core reference
 184                 voltage from the vid pins.
 185
 186 Also see the Alarms section for status flags associated with voltages.
 187
 188
 189 ********
 190 * Fans *
 191 ********
 192
 193 fan[1-*]_min    Fan minimum value
 194                 Unit: revolution/min (RPM)
 195                 RW
 196
 197 fan[1-*]_max    Fan maximum value
 198                 Unit: revolution/min (RPM)
 199                 Only rarely supported by the hardware.
 200                 RW
 201
 202 fan[1-*]_input  Fan input value.
 203                 Unit: revolution/min (RPM)
 204                 RO
 205
 206 fan[1-*]_div    Fan divisor.
 207                 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
 208                 RW
 209                 Some chips only support values 1, 2, 4 and 8.
 210                 Note that this is actually an internal clock divisor, which
 211                 affects the measurable speed range, not the read value.
 212
 213 fan[1-*]_pulses Number of tachometer pulses per fan revolution.
 214                 Integer value, typically between 1 and 4.
 215                 RW
 216                 This value is a characteristic of the fan connected to the
 217                 device's input, so it has to be set in accordance with the fan
 218                 model.
 219                 Should only be created if the chip has a register to configure
 220                 the number of pulses. In the absence of such a register (and
 221                 thus attribute) the value assumed by all devices is 2 pulses
 222                 per fan revolution.
 223
 224 fan[1-*]_target
 225                 Desired fan speed
 226                 Unit: revolution/min (RPM)
 227                 RW
 228                 Only makes sense if the chip supports closed-loop fan speed
 229                 control based on the measured fan speed.
 230
 231 fan[1-*]_label  Suggested fan channel label.
 232                 Text string
 233                 Should only be created if the driver has hints about what
 234                 this fan channel is being used for, and user-space doesn't.
 235                 In all other cases, the label is provided by user-space.
 236                 RO
 237
 238 Also see the Alarms section for status flags associated with fans.
 239
 240
 241 *******
 242 * PWM *
 243 *******
 244
 245 pwm[1-*]        Pulse width modulation fan control.
 246                 Integer value in the range 0 to 255
 247                 RW
 248                 255 is max or 100%.
 249
 250 pwm[1-*]_enable
 251                 Fan speed control method:
 252                 0: no fan speed control (i.e. fan at full speed)
 253                 1: manual fan speed control enabled (using pwm[1-*])
 254                 2+: automatic fan speed control enabled
 255                 Check individual chip documentation files for automatic mode
 256                 details.
 257                 RW
 258
 259 pwm[1-*]_mode   0: DC mode (direct current)
 260                 1: PWM mode (pulse-width modulation)
 261                 RW
 262
 263 pwm[1-*]_freq   Base PWM frequency in Hz.
 264                 Only possibly available when pwmN_mode is PWM, but not always
 265                 present even then.
 266                 RW
 267
 268 pwm[1-*]_auto_channels_temp
 269                 Select which temperature channels affect this PWM output in
 270                 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
 271                 Which values are possible depend on the chip used.
 272                 RW
 273
 274 pwm[1-*]_auto_point[1-*]_pwm
 275 pwm[1-*]_auto_point[1-*]_temp
 276 pwm[1-*]_auto_point[1-*]_temp_hyst
 277                 Define the PWM vs temperature curve. Number of trip points is
 278                 chip-dependent. Use this for chips which associate trip points
 279                 to PWM output channels.
 280                 RW
 281
 282 temp[1-*]_auto_point[1-*]_pwm
 283 temp[1-*]_auto_point[1-*]_temp
 284 temp[1-*]_auto_point[1-*]_temp_hyst
 285                 Define the PWM vs temperature curve. Number of trip points is
 286                 chip-dependent. Use this for chips which associate trip points
 287                 to temperature channels.
 288                 RW
 289
 290 There is a third case where trip points are associated to both PWM output
 291 channels and temperature channels: the PWM values are associated to PWM
 292 output channels while the temperature values are associated to temperature
 293 channels. In that case, the result is determined by the mapping between
 294 temperature inputs and PWM outputs. When several temperature inputs are
 295 mapped to a given PWM output, this leads to several candidate PWM values.
 296 The actual result is up to the chip, but in general the highest candidate
 297 value (fastest fan speed) wins.
 298
 299
 300 ****************
 301 * Temperatures *
 302 ****************
 303
 304 temp[1-*]_type  Sensor type selection.
 305                 Integers 1 to 6
 306                 RW
 307                 1: CPU embedded diode
 308                 2: 3904 transistor
 309                 3: thermal diode
 310                 4: thermistor
 311                 5: AMD AMDSI
 312                 6: Intel PECI
 313                 Not all types are supported by all chips
 314
 315 temp[1-*]_max   Temperature max value.
 316                 Unit: millidegree Celsius (or millivolt, see below)
 317                 RW
 318
 319 temp[1-*]_min   Temperature min value.
 320                 Unit: millidegree Celsius
 321                 RW
 322
 323 temp[1-*]_max_hyst
 324                 Temperature hysteresis value for max limit.
 325                 Unit: millidegree Celsius
 326                 Must be reported as an absolute temperature, NOT a delta
 327                 from the max value.
 328                 RW
 329
 330 temp[1-*]_min_hyst
 331                 Temperature hysteresis value for min limit.
 332                 Unit: millidegree Celsius
 333                 Must be reported as an absolute temperature, NOT a delta
 334                 from the min value.
 335                 RW
 336
 337 temp[1-*]_input Temperature input value.
 338                 Unit: millidegree Celsius
 339                 RO
 340
 341 temp[1-*]_crit  Temperature critical max value, typically greater than
 342                 corresponding temp_max values.
 343                 Unit: millidegree Celsius
 344                 RW
 345
 346 temp[1-*]_crit_hyst
 347                 Temperature hysteresis value for critical limit.
 348                 Unit: millidegree Celsius
 349                 Must be reported as an absolute temperature, NOT a delta
 350                 from the critical value.
 351                 RW
 352
 353 temp[1-*]_emergency
 354                 Temperature emergency max value, for chips supporting more than
 355                 two upper temperature limits. Must be equal or greater than
 356                 corresponding temp_crit values.
 357                 Unit: millidegree Celsius
 358                 RW
 359
 360 temp[1-*]_emergency_hyst
 361                 Temperature hysteresis value for emergency limit.
 362                 Unit: millidegree Celsius
 363                 Must be reported as an absolute temperature, NOT a delta
 364                 from the emergency value.
 365                 RW
 366
 367 temp[1-*]_lcrit Temperature critical min value, typically lower than
 368                 corresponding temp_min values.
 369                 Unit: millidegree Celsius
 370                 RW
 371
 372 temp[1-*]_lcrit_hyst
 373                 Temperature hysteresis value for critical min limit.
 374                 Unit: millidegree Celsius
 375                 Must be reported as an absolute temperature, NOT a delta
 376                 from the critical min value.
 377                 RW
 378
 379 temp[1-*]_offset
 380                 Temperature offset which is added to the temperature reading
 381                 by the chip.
 382                 Unit: millidegree Celsius
 383                 Read/Write value.
 384
 385 temp[1-*]_label Suggested temperature channel label.
 386                 Text string
 387                 Should only be created if the driver has hints about what
 388                 this temperature channel is being used for, and user-space
 389                 doesn't. In all other cases, the label is provided by
 390                 user-space.
 391                 RO
 392
 393 temp[1-*]_lowest
 394                 Historical minimum temperature
 395                 Unit: millidegree Celsius
 396                 RO
 397
 398 temp[1-*]_highest
 399                 Historical maximum temperature
 400                 Unit: millidegree Celsius
 401                 RO
 402
 403 temp[1-*]_reset_history
 404                 Reset temp_lowest and temp_highest
 405                 WO
 406
 407 temp_reset_history
 408                 Reset temp_lowest and temp_highest for all sensors
 409                 WO
 410
 411 Some chips measure temperature using external thermistors and an ADC, and
 412 report the temperature measurement as a voltage. Converting this voltage
 413 back to a temperature (or the other way around for limits) requires
 414 mathematical functions not available in the kernel, so the conversion
 415 must occur in user space. For these chips, all temp* files described
 416 above should contain values expressed in millivolt instead of millidegree
 417 Celsius. In other words, such temperature channels are handled as voltage
 418 channels by the driver.
 419
 420 Also see the Alarms section for status flags associated with temperatures.
 421
 422
 423 ************
 424 * Currents *
 425 ************
 426
 427 curr[1-*]_max   Current max value
 428                 Unit: milliampere
 429                 RW
 430
 431 curr[1-*]_min   Current min value.
 432                 Unit: milliampere
 433                 RW
 434
 435 curr[1-*]_lcrit Current critical low value
 436                 Unit: milliampere
 437                 RW
 438
 439 curr[1-*]_crit  Current critical high value.
 440                 Unit: milliampere
 441                 RW
 442
 443 curr[1-*]_input Current input value
 444                 Unit: milliampere
 445                 RO
 446
 447 curr[1-*]_average
 448                 Average current use
 449                 Unit: milliampere
 450                 RO
 451
 452 curr[1-*]_lowest
 453                 Historical minimum current
 454                 Unit: milliampere
 455                 RO
 456
 457 curr[1-*]_highest
 458                 Historical maximum current
 459                 Unit: milliampere
 460                 RO
 461
 462 curr[1-*]_reset_history
 463                 Reset currX_lowest and currX_highest
 464                 WO
 465
 466 curr_reset_history
 467                 Reset currX_lowest and currX_highest for all sensors
 468                 WO
 469
 470 Also see the Alarms section for status flags associated with currents.
 471
 472 *********
 473 * Power *
 474 *********
 475
 476 power[1-*]_average              Average power use
 477                                 Unit: microWatt
 478                                 RO
 479
 480 power[1-*]_average_interval     Power use averaging interval.  A poll
 481                                 notification is sent to this file if the
 482                                 hardware changes the averaging interval.
 483                                 Unit: milliseconds
 484                                 RW
 485
 486 power[1-*]_average_interval_max Maximum power use averaging interval
 487                                 Unit: milliseconds
 488                                 RO
 489
 490 power[1-*]_average_interval_min Minimum power use averaging interval
 491                                 Unit: milliseconds
 492                                 RO
 493
 494 power[1-*]_average_highest      Historical average maximum power use
 495                                 Unit: microWatt
 496                                 RO
 497
 498 power[1-*]_average_lowest       Historical average minimum power use
 499                                 Unit: microWatt
 500                                 RO
 501
 502 power[1-*]_average_max          A poll notification is sent to
 503                                 power[1-*]_average when power use
 504                                 rises above this value.
 505                                 Unit: microWatt
 506                                 RW
 507
 508 power[1-*]_average_min          A poll notification is sent to
 509                                 power[1-*]_average when power use
 510                                 sinks below this value.
 511                                 Unit: microWatt
 512                                 RW
 513
 514 power[1-*]_input                Instantaneous power use
 515                                 Unit: microWatt
 516                                 RO
 517
 518 power[1-*]_input_highest        Historical maximum power use
 519                                 Unit: microWatt
 520                                 RO
 521
 522 power[1-*]_input_lowest         Historical minimum power use
 523                                 Unit: microWatt
 524                                 RO
 525
 526 power[1-*]_reset_history        Reset input_highest, input_lowest,
 527                                 average_highest and average_lowest.
 528                                 WO
 529
 530 power[1-*]_accuracy             Accuracy of the power meter.
 531                                 Unit: Percent
 532                                 RO
 533
 534 power[1-*]_cap                  If power use rises above this limit, the
 535                                 system should take action to reduce power use.
 536                                 A poll notification is sent to this file if the
 537                                 cap is changed by the hardware.  The *_cap
 538                                 files only appear if the cap is known to be
 539                                 enforced by hardware.
 540                                 Unit: microWatt
 541                                 RW
 542
 543 power[1-*]_cap_hyst             Margin of hysteresis built around capping and
 544                                 notification.
 545                                 Unit: microWatt
 546                                 RW
 547
 548 power[1-*]_cap_max              Maximum cap that can be set.
 549                                 Unit: microWatt
 550                                 RO
 551
 552 power[1-*]_cap_min              Minimum cap that can be set.
 553                                 Unit: microWatt
 554                                 RO
 555
 556 power[1-*]_max                  Maximum power.
 557                                 Unit: microWatt
 558                                 RW
 559
 560 power[1-*]_crit                 Critical maximum power.
 561                                 If power rises to or above this limit, the
 562                                 system is expected take drastic action to reduce
 563                                 power consumption, such as a system shutdown or
 564                                 a forced powerdown of some devices.
 565                                 Unit: microWatt
 566                                 RW
 567
 568 Also see the Alarms section for status flags associated with power readings.
 569
 570 **********
 571 * Energy *
 572 **********
 573
 574 energy[1-*]_input               Cumulative energy use
 575                                 Unit: microJoule
 576                                 RO
 577
 578
 579 ************
 580 * Humidity *
 581 ************
 582
 583 humidity[1-*]_input             Humidity
 584                                 Unit: milli-percent (per cent mille, pcm)
 585                                 RO
 586
 587
 588 **********
 589 * Alarms *
 590 **********
 591
 592 Each channel or limit may have an associated alarm file, containing a
 593 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
 594
 595 Usually a given chip will either use channel-related alarms, or
 596 limit-related alarms, not both. The driver should just reflect the hardware
 597 implementation.
 598
 599 in[0-*]_alarm
 600 curr[1-*]_alarm
 601 power[1-*]_alarm
 602 fan[1-*]_alarm
 603 temp[1-*]_alarm
 604                 Channel alarm
 605                 0: no alarm
 606                 1: alarm
 607                 RO
 608
 609 OR
 610
 611 in[0-*]_min_alarm
 612 in[0-*]_max_alarm
 613 in[0-*]_lcrit_alarm
 614 in[0-*]_crit_alarm
 615 curr[1-*]_min_alarm
 616 curr[1-*]_max_alarm
 617 curr[1-*]_lcrit_alarm
 618 curr[1-*]_crit_alarm
 619 power[1-*]_cap_alarm
 620 power[1-*]_max_alarm
 621 power[1-*]_crit_alarm
 622 fan[1-*]_min_alarm
 623 fan[1-*]_max_alarm
 624 temp[1-*]_min_alarm
 625 temp[1-*]_max_alarm
 626 temp[1-*]_lcrit_alarm
 627 temp[1-*]_crit_alarm
 628 temp[1-*]_emergency_alarm
 629                 Limit alarm
 630                 0: no alarm
 631                 1: alarm
 632                 RO
 633
 634 Each input channel may have an associated fault file. This can be used
 635 to notify open diodes, unconnected fans etc. where the hardware
 636 supports it. When this boolean has value 1, the measurement for that
 637 channel should not be trusted.
 638
 639 fan[1-*]_fault
 640 temp[1-*]_fault
 641                 Input fault condition
 642                 0: no fault occurred
 643                 1: fault condition
 644                 RO
 645
 646 Some chips also offer the possibility to get beeped when an alarm occurs:
 647
 648 beep_enable     Master beep enable
 649                 0: no beeps
 650                 1: beeps
 651                 RW
 652
 653 in[0-*]_beep
 654 curr[1-*]_beep
 655 fan[1-*]_beep
 656 temp[1-*]_beep
 657                 Channel beep
 658                 0: disable
 659                 1: enable
 660                 RW
 661
 662 In theory, a chip could provide per-limit beep masking, but no such chip
 663 was seen so far.
 664
 665 Old drivers provided a different, non-standard interface to alarms and
 666 beeps. These interface files are deprecated, but will be kept around
 667 for compatibility reasons:
 668
 669 alarms          Alarm bitmask.
 670                 RO
 671                 Integer representation of one to four bytes.
 672                 A '1' bit means an alarm.
 673                 Chips should be programmed for 'comparator' mode so that
 674                 the alarm will 'come back' after you read the register
 675                 if it is still valid.
 676                 Generally a direct representation of a chip's internal
 677                 alarm registers; there is no standard for the position
 678                 of individual bits. For this reason, the use of this
 679                 interface file for new drivers is discouraged. Use
 680                 individual *_alarm and *_fault files instead.
 681                 Bits are defined in kernel/include/sensors.h.
 682
 683 beep_mask       Bitmask for beep.
 684                 Same format as 'alarms' with the same bit locations,
 685                 use discouraged for the same reason. Use individual
 686                 *_beep files instead.
 687                 RW
 688
 689
 690 ***********************
 691 * Intrusion detection *
 692 ***********************
 693
 694 intrusion[0-*]_alarm
 695                 Chassis intrusion detection
 696                 0: OK
 697                 1: intrusion detected
 698                 RW
 699                 Contrary to regular alarm flags which clear themselves
 700                 automatically when read, this one sticks until cleared by
 701                 the user. This is done by writing 0 to the file. Writing
 702                 other values is unsupported.
 703
 704 intrusion[0-*]_beep
 705                 Chassis intrusion beep
 706                 0: disable
 707                 1: enable
 708                 RW
 709
 710
 711 sysfs attribute writes interpretation
 712 -------------------------------------
 713
 714 hwmon sysfs attributes always contain numbers, so the first thing to do is to
 715 convert the input to a number, there are 2 ways todo this depending whether
 716 the number can be negative or not:
 717 unsigned long u = simple_strtoul(buf, NULL, 10);
 718 long s = simple_strtol(buf, NULL, 10);
 719
 720 With buf being the buffer with the user input being passed by the kernel.
 721 Notice that we do not use the second argument of strto[u]l, and thus cannot
 722 tell when 0 is returned, if this was really 0 or is caused by invalid input.
 723 This is done deliberately as checking this everywhere would add a lot of
 724 code to the kernel.
 725
 726 Notice that it is important to always store the converted value in an
 727 unsigned long or long, so that no wrap around can happen before any further
 728 checking.
 729
 730 After the input string is converted to an (unsigned) long, the value should be
 731 checked if its acceptable. Be careful with further conversions on the value
 732 before checking it for validity, as these conversions could still cause a wrap
 733 around before the check. For example do not multiply the result, and only
 734 add/subtract if it has been divided before the add/subtract.
 735
 736 What to do if a value is found to be invalid, depends on the type of the
 737 sysfs attribute that is being set. If it is a continuous setting like a
 738 tempX_max or inX_max attribute, then the value should be clamped to its
 739 limits using clamp_val(value, min_limit, max_limit). If it is not continuous
 740 like for example a tempX_type, then when an invalid value is written,
 741 -EINVAL should be returned.
 742
 743 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
 744
 745         long v = simple_strtol(buf, NULL, 10) / 1000;
 746         v = clamp_val(v, -128, 127);
 747         /* write v to register */
 748
 749 Example2, fan divider setting, valid values 2, 4 and 8:
 750
 751         unsigned long v = simple_strtoul(buf, NULL, 10);
 752
 753         switch (v) {
 754         case 2: v = 1; break;
 755         case 4: v = 2; break;
 756         case 8: v = 3; break;
 757         default:
 758                 return -EINVAL;
 759         }
 760         /* write v to register */