/Documentation/hwmon/sysfs-interface
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1Naming and data format standards for sysfs files
2------------------------------------------------
3
4The libsensors library offers an interface to the raw sensors data
5through the sysfs interface. Since lm-sensors 3.0.0, libsensors is
6completely chip-independent. It assumes that all the kernel drivers
7implement the standard sysfs interface described in this document.
8This makes adding or updating support for any given chip very easy, as
9libsensors, and applications using it, do not need to be modified.
10This is a major improvement compared to lm-sensors 2.
11
12Note that motherboards vary widely in the connections to sensor chips.
13There is no standard that ensures, for example, that the second
14temperature sensor is connected to the CPU, or that the second fan is on
15the CPU. Also, some values reported by the chips need some computation
16before they make full sense. For example, most chips can only measure
17voltages between 0 and +4V. Other voltages are scaled back into that
18range using external resistors. Since the values of these resistors
19can change from motherboard to motherboard, the conversions cannot be
20hard coded into the driver and have to be done in user space.
21
22For this reason, even if we aim at a chip-independent libsensors, it will
23still require a configuration file (e.g. /etc/sensors.conf) for proper
24values conversion, labeling of inputs and hiding of unused inputs.
25
26An alternative method that some programs use is to access the sysfs
27files directly. This document briefly describes the standards that the
28drivers follow, so that an application program can scan for entries and
29access this data in a simple and consistent way. That said, such programs
30will have to implement conversion, labeling and hiding of inputs. For
31this reason, it is still not recommended to bypass the library.
32
33Each chip gets its own directory in the sysfs /sys/devices tree. To
34find all sensor chips, it is easier to follow the device symlinks from
35/sys/class/hwmon/hwmon*.
36
37Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
38in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
39in the hwmon "class" device directory are also supported. Complex drivers
40(e.g. drivers for multifunction chips) may want to use this possibility to
41avoid namespace pollution. The only drawback will be that older versions of
42libsensors won't support the driver in question.
43
44All sysfs values are fixed point numbers.
45
46There is only one value per file, unlike the older /proc specification.
47The common scheme for files naming is: <type><number>_<item>. Usual
48types for sensor chips are "in" (voltage), "temp" (temperature) and
49"fan" (fan). Usual items are "input" (measured value), "max" (high
50threshold, "min" (low threshold). Numbering usually starts from 1,
51except for voltages which start from 0 (because most data sheets use
52this). A number is always used for elements that can be present more
53than once, even if there is a single element of the given type on the
54specific chip. Other files do not refer to a specific element, so
55they have a simple name, and no number.
56
57Alarms are direct indications read from the chips. The drivers do NOT
58make comparisons of readings to thresholds. This allows violations
59between readings to be caught and alarmed. The exact definition of an
60alarm (for example, whether a threshold must be met or must be exceeded
61to cause an alarm) is chip-dependent.
62
63When setting values of hwmon sysfs attributes, the string representation of
64the desired value must be written, note that strings which are not a number
65are 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
72RO read only value
73WO write only value
74RW read/write value
75
76Read/write values may be read-only for some chips, depending on the
77hardware implementation.
78
79All entries (except name) are optional, and should only be created in a
80given driver if the chip has the feature.
81
82
83*********************
84* Global attributes *
85*********************
86
87name 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
94update_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
106in[0-*]_min Voltage min value.
107 Unit: millivolt
108 RW
109
110in[0-*]_max Voltage max value.
111 Unit: millivolt
112 RW
113
114in[0-*]_input Voltage input value.
115 Unit: millivolt
116 RO
117 Voltage measured on the chip pin.
118 Actual voltage depends on the scaling resistors on the
119 motherboard, as recommended in the chip datasheet.
120 This varies by chip and by motherboard.
121 Because of this variation, values are generally NOT scaled
122 by the chip driver, and must be done by the application.
123 However, some drivers (notably lm87 and via686a)
124 do scale, because of internal resistors built into a chip.
125 These drivers will output the actual voltage. Rule of
126 thumb: drivers should report the voltage values at the
127 "pins" of the chip.
128
129in[0-*]_label Suggested voltage channel label.
130 Text string
131 Should only be created if the driver has hints about what
132 this voltage channel is being used for, and user-space
133 doesn't. In all other cases, the label is provided by
134 user-space.
135 RO
136
137cpu[0-*]_vid CPU core reference voltage.
138 Unit: millivolt
139 RO
140 Not always correct.
141
142vrm Voltage Regulator Module version number.
143 RW (but changing it should no more be necessary)
144 Originally the VRM standard version multiplied by 10, but now
145 an arbitrary number, as not all standards have a version
146 number.
147 Affects the way the driver calculates the CPU core reference
148 voltage from the vid pins.
149
150Also see the Alarms section for status flags associated with voltages.
151
152
153********
154* Fans *
155********
156
157fan[1-*]_min Fan minimum value
158 Unit: revolution/min (RPM)
159 RW
160
161fan[1-*]_max Fan maximum value
162 Unit: revolution/min (RPM)
163 Only rarely supported by the hardware.
164 RW
165
166fan[1-*]_input Fan input value.
167 Unit: revolution/min (RPM)
168 RO
169
170fan[1-*]_div Fan divisor.
171 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
172 RW
173 Some chips only support values 1, 2, 4 and 8.
174 Note that this is actually an internal clock divisor, which
175 affects the measurable speed range, not the read value.
176
177fan[1-*]_target
178 Desired fan speed
179 Unit: revolution/min (RPM)
180 RW
181 Only makes sense if the chip supports closed-loop fan speed
182 control based on the measured fan speed.
183
184fan[1-*]_label Suggested fan channel label.
185 Text string
186 Should only be created if the driver has hints about what
187 this fan channel is being used for, and user-space doesn't.
188 In all other cases, the label is provided by user-space.
189 RO
190
191Also see the Alarms section for status flags associated with fans.
192
193
194*******
195* PWM *
196*******
197
198pwm[1-*] Pulse width modulation fan control.
199 Integer value in the range 0 to 255
200 RW
201 255 is max or 100%.
202
203pwm[1-*]_enable
204 Fan speed control method:
205 0: no fan speed control (i.e. fan at full speed)
206 1: manual fan speed control enabled (using pwm[1-*])
207 2+: automatic fan speed control enabled
208 Check individual chip documentation files for automatic mode
209 details.
210 RW
211
212pwm[1-*]_mode 0: DC mode (direct current)
213 1: PWM mode (pulse-width modulation)
214 RW
215
216pwm[1-*]_freq Base PWM frequency in Hz.
217 Only possibly available when pwmN_mode is PWM, but not always
218 present even then.
219 RW
220
221pwm[1-*]_auto_channels_temp
222 Select which temperature channels affect this PWM output in
223 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
224 Which values are possible depend on the chip used.
225 RW
226
227pwm[1-*]_auto_point[1-*]_pwm
228pwm[1-*]_auto_point[1-*]_temp
229pwm[1-*]_auto_point[1-*]_temp_hyst
230 Define the PWM vs temperature curve. Number of trip points is
231 chip-dependent. Use this for chips which associate trip points
232 to PWM output channels.
233 RW
234
235temp[1-*]_auto_point[1-*]_pwm
236temp[1-*]_auto_point[1-*]_temp
237temp[1-*]_auto_point[1-*]_temp_hyst
238 Define the PWM vs temperature curve. Number of trip points is
239 chip-dependent. Use this for chips which associate trip points
240 to temperature channels.
241 RW
242
243There is a third case where trip points are associated to both PWM output
244channels and temperature channels: the PWM values are associated to PWM
245output channels while the temperature values are associated to temperature
246channels. In that case, the result is determined by the mapping between
247temperature inputs and PWM outputs. When several temperature inputs are
248mapped to a given PWM output, this leads to several candidate PWM values.
249The actual result is up to the chip, but in general the highest candidate
250value (fastest fan speed) wins.
251
252
253****************
254* Temperatures *
255****************
256
257temp[1-*]_type Sensor type selection.
258 Integers 1 to 6
259 RW
260 1: PII/Celeron Diode
261 2: 3904 transistor
262 3: thermal diode
263 4: thermistor
264 5: AMD AMDSI
265 6: Intel PECI
266 Not all types are supported by all chips
267
268temp[1-*]_max Temperature max value.
269 Unit: millidegree Celsius (or millivolt, see below)
270 RW
271
272temp[1-*]_min Temperature min value.
273 Unit: millidegree Celsius
274 RW
275
276temp[1-*]_max_hyst
277 Temperature hysteresis value for max limit.
278 Unit: millidegree Celsius
279 Must be reported as an absolute temperature, NOT a delta
280 from the max value.
281 RW
282
283temp[1-*]_input Temperature input value.
284 Unit: millidegree Celsius
285 RO
286
287temp[1-*]_crit Temperature critical value, typically greater than
288 corresponding temp_max values.
289 Unit: millidegree Celsius
290 RW
291
292temp[1-*]_crit_hyst
293 Temperature hysteresis value for critical limit.
294 Unit: millidegree Celsius
295 Must be reported as an absolute temperature, NOT a delta
296 from the critical value.
297 RW
298
299temp[1-*]_offset
300 Temperature offset which is added to the temperature reading
301 by the chip.
302 Unit: millidegree Celsius
303 Read/Write value.
304
305temp[1-*]_label Suggested temperature channel label.
306 Text string
307 Should only be created if the driver has hints about what
308 this temperature channel is being used for, and user-space
309 doesn't. In all other cases, the label is provided by
310 user-space.
311 RO
312
313temp[1-*]_lowest
314 Historical minimum temperature
315 Unit: millidegree Celsius
316 RO
317
318temp[1-*]_highest
319 Historical maximum temperature
320 Unit: millidegree Celsius
321 RO
322
323temp[1-*]_reset_history
324 Reset temp_lowest and temp_highest
325 WO
326
327temp_reset_history
328 Reset temp_lowest and temp_highest for all sensors
329 WO
330
331Some chips measure temperature using external thermistors and an ADC, and
332report the temperature measurement as a voltage. Converting this voltage
333back to a temperature (or the other way around for limits) requires
334mathematical functions not available in the kernel, so the conversion
335must occur in user space. For these chips, all temp* files described
336above should contain values expressed in millivolt instead of millidegree
337Celsius. In other words, such temperature channels are handled as voltage
338channels by the driver.
339
340Also see the Alarms section for status flags associated with temperatures.
341
342
343************
344* Currents *
345************
346
347Note that no known chip provides current measurements as of writing,
348so this part is theoretical, so to say.
349
350curr[1-*]_max Current max value
351 Unit: milliampere
352 RW
353
354curr[1-*]_min Current min value.
355 Unit: milliampere
356 RW
357
358curr[1-*]_input Current input value
359 Unit: milliampere
360 RO
361
362*********
363* Power *
364*********
365
366power[1-*]_average Average power use
367 Unit: microWatt
368 RO
369
370power[1-*]_average_interval Power use averaging interval. A poll
371 notification is sent to this file if the
372 hardware changes the averaging interval.
373 Unit: milliseconds
374 RW
375
376power[1-*]_average_interval_max Maximum power use averaging interval
377 Unit: milliseconds
378 RO
379
380power[1-*]_average_interval_min Minimum power use averaging interval
381 Unit: milliseconds
382 RO
383
384power[1-*]_average_highest Historical average maximum power use
385 Unit: microWatt
386 RO
387
388power[1-*]_average_lowest Historical average minimum power use
389 Unit: microWatt
390 RO
391
392power[1-*]_average_max A poll notification is sent to
393 power[1-*]_average when power use
394 rises above this value.
395 Unit: microWatt
396 RW
397
398power[1-*]_average_min A poll notification is sent to
399 power[1-*]_average when power use
400 sinks below this value.
401 Unit: microWatt
402 RW
403
404power[1-*]_input Instantaneous power use
405 Unit: microWatt
406 RO
407
408power[1-*]_input_highest Historical maximum power use
409 Unit: microWatt
410 RO
411
412power[1-*]_input_lowest Historical minimum power use
413 Unit: microWatt
414 RO
415
416power[1-*]_reset_history Reset input_highest, input_lowest,
417 average_highest and average_lowest.
418 WO
419
420power[1-*]_accuracy Accuracy of the power meter.
421 Unit: Percent
422 RO
423
424power[1-*]_alarm 1 if the system is drawing more power than the
425 cap allows; 0 otherwise. A poll notification is
426 sent to this file when the power use exceeds the
427 cap. This file only appears if the cap is known
428 to be enforced by hardware.
429 RO
430
431power[1-*]_cap If power use rises above this limit, the
432 system should take action to reduce power use.
433 A poll notification is sent to this file if the
434 cap is changed by the hardware. The *_cap
435 files only appear if the cap is known to be
436 enforced by hardware.
437 Unit: microWatt
438 RW
439
440power[1-*]_cap_hyst Margin of hysteresis built around capping and
441 notification.
442 Unit: microWatt
443 RW
444
445power[1-*]_cap_max Maximum cap that can be set.
446 Unit: microWatt
447 RO
448
449power[1-*]_cap_min Minimum cap that can be set.
450 Unit: microWatt
451 RO
452
453**********
454* Energy *
455**********
456
457energy[1-*]_input Cumulative energy use
458 Unit: microJoule
459 RO
460
461
462**********
463* Alarms *
464**********
465
466Each channel or limit may have an associated alarm file, containing a
467boolean value. 1 means than an alarm condition exists, 0 means no alarm.
468
469Usually a given chip will either use channel-related alarms, or
470limit-related alarms, not both. The driver should just reflect the hardware
471implementation.
472
473in[0-*]_alarm
474fan[1-*]_alarm
475temp[1-*]_alarm
476 Channel alarm
477 0: no alarm
478 1: alarm
479 RO
480
481OR
482
483in[0-*]_min_alarm
484in[0-*]_max_alarm
485fan[1-*]_min_alarm
486fan[1-*]_max_alarm
487temp[1-*]_min_alarm
488temp[1-*]_max_alarm
489temp[1-*]_crit_alarm
490 Limit alarm
491 0: no alarm
492 1: alarm
493 RO
494
495Each input channel may have an associated fault file. This can be used
496to notify open diodes, unconnected fans etc. where the hardware
497supports it. When this boolean has value 1, the measurement for that
498channel should not be trusted.
499
500in[0-*]_fault
501fan[1-*]_fault
502temp[1-*]_fault
503 Input fault condition
504 0: no fault occured
505 1: fault condition
506 RO
507
508Some chips also offer the possibility to get beeped when an alarm occurs:
509
510beep_enable Master beep enable
511 0: no beeps
512 1: beeps
513 RW
514
515in[0-*]_beep
516fan[1-*]_beep
517temp[1-*]_beep
518 Channel beep
519 0: disable
520 1: enable
521 RW
522
523In theory, a chip could provide per-limit beep masking, but no such chip
524was seen so far.
525
526Old drivers provided a different, non-standard interface to alarms and
527beeps. These interface files are deprecated, but will be kept around
528for compatibility reasons:
529
530alarms Alarm bitmask.
531 RO
532 Integer representation of one to four bytes.
533 A '1' bit means an alarm.
534 Chips should be programmed for 'comparator' mode so that
535 the alarm will 'come back' after you read the register
536 if it is still valid.
537 Generally a direct representation of a chip's internal
538 alarm registers; there is no standard for the position
539 of individual bits. For this reason, the use of this
540 interface file for new drivers is discouraged. Use
541 individual *_alarm and *_fault files instead.
542 Bits are defined in kernel/include/sensors.h.
543
544beep_mask Bitmask for beep.
545 Same format as 'alarms' with the same bit locations,
546 use discouraged for the same reason. Use individual
547 *_beep files instead.
548 RW
549
550
551***********************
552* Intrusion detection *
553***********************
554
555intrusion[0-*]_alarm
556 Chassis intrusion detection
557 0: OK
558 1: intrusion detected
559 RW
560 Contrary to regular alarm flags which clear themselves
561 automatically when read, this one sticks until cleared by
562 the user. This is done by writing 0 to the file. Writing
563 other values is unsupported.
564
565intrusion[0-*]_beep
566 Chassis intrusion beep
567 0: disable
568 1: enable
569 RW
570
571
572sysfs attribute writes interpretation
573-------------------------------------
574
575hwmon sysfs attributes always contain numbers, so the first thing to do is to
576convert the input to a number, there are 2 ways todo this depending whether
577the number can be negative or not:
578unsigned long u = simple_strtoul(buf, NULL, 10);
579long s = simple_strtol(buf, NULL, 10);
580
581With buf being the buffer with the user input being passed by the kernel.
582Notice that we do not use the second argument of strto[u]l, and thus cannot
583tell when 0 is returned, if this was really 0 or is caused by invalid input.
584This is done deliberately as checking this everywhere would add a lot of
585code to the kernel.
586
587Notice that it is important to always store the converted value in an
588unsigned long or long, so that no wrap around can happen before any further
589checking.
590
591After the input string is converted to an (unsigned) long, the value should be
592checked if its acceptable. Be careful with further conversions on the value
593before checking it for validity, as these conversions could still cause a wrap
594around before the check. For example do not multiply the result, and only
595add/subtract if it has been divided before the add/subtract.
596
597What to do if a value is found to be invalid, depends on the type of the
598sysfs attribute that is being set. If it is a continuous setting like a
599tempX_max or inX_max attribute, then the value should be clamped to its
600limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
601continuous like for example a tempX_type, then when an invalid value is
602written, -EINVAL should be returned.
603
604Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
605
606 long v = simple_strtol(buf, NULL, 10) / 1000;
607 v = SENSORS_LIMIT(v, -128, 127);
608 /* write v to register */
609
610Example2, fan divider setting, valid values 2, 4 and 8:
611
612 unsigned long v = simple_strtoul(buf, NULL, 10);
613
614 switch (v) {
615 case 2: v = 1; break;
616 case 4: v = 2; break;
617 case 8: v = 3; break;
618 default:
619 return -EINVAL;
620 }
621 /* write v to register */