Documentation/i2c/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. See libsensors documentation and source for
   6 more further information. As of writing this document, libsensors
   7 (from lm_sensors 2.8.3) is heavily chip-dependant. Adding or updating
   8 support for any given chip requires modifying the library's code.
   9 This is because libsensors was written for the procfs interface
  10 older kernel modules were using, which wasn't standardized enough.
  11 Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
  12 support for the sysfs interface, though.
  13
  14 The new sysfs interface was designed to be as chip-independant as
  15 possible.
  16
  17 Note that motherboards vary widely in the connections to sensor chips.
  18 There is no standard that ensures, for example, that the second
  19 temperature sensor is connected to the CPU, or that the second fan is on
  20 the CPU. Also, some values reported by the chips need some computation
  21 before they make full sense. For example, most chips can only measure
  22 voltages between 0 and +4V. Other voltages are scaled back into that
  23 range using external resistors. Since the values of these resistors
  24 can change from motherboard to motherboard, the conversions cannot be
  25 hard coded into the driver and have to be done in user space.
  26
  27 For this reason, even if we aim at a chip-independant libsensors, it will
  28 still require a configuration file (e.g. /etc/sensors.conf) for proper
  29 values conversion, labeling of inputs and hiding of unused inputs.
  30
  31 An alternative method that some programs use is to access the sysfs
  32 files directly. This document briefly describes the standards that the
  33 drivers follow, so that an application program can scan for entries and
  34 access this data in a simple and consistent way. That said, such programs
  35 will have to implement conversion, labeling and hiding of inputs. For
  36 this reason, it is still not recommended to bypass the library.
  37
  38 If you are developing a userspace application please send us feedback on
  39 this standard.
  40
  41 Note that this standard isn't completely established yet, so it is subject
  42 to changes, even important ones. One more reason to use the library instead
  43 of accessing sysfs files directly.
  44
  45 Each chip gets its own directory in the sysfs /sys/devices tree.  To
  46 find all sensor chips, it is easier to follow the symlinks from
  47 /sys/i2c/devices/
  48
  49 All sysfs values are fixed point numbers.  To get the true value of some
  50 of the values, you should divide by the specified value.
  51
  52 There is only one value per file, unlike the older /proc specification.
  53 The common scheme for files naming is: <type><number>_<item>. Usual
  54 types for sensor chips are "in" (voltage), "temp" (temperature) and
  55 "fan" (fan). Usual items are "input" (measured value), "max" (high
  56 threshold, "min" (low threshold). Numbering usually starts from 1,
  57 except for voltages which start from 0 (because most data sheets use
  58 this). A number is always used for elements that can be present more
  59 than once, even if there is a single element of the given type on the
  60 specific chip. Other files do not refer to a specific element, so
  61 they have a simple name, and no number.
  62
  63 Alarms are direct indications read from the chips. The drivers do NOT
  64 make comparisons of readings to thresholds. This allows violations
  65 between readings to be caught and alarmed. The exact definition of an
  66 alarm (for example, whether a threshold must be met or must be exceeded
  67 to cause an alarm) is chip-dependent.
  68
  69
  70 -------------------------------------------------------------------------
  71
  72 ************
  73 * Voltages *
  74 ************
  75
  76 in[0-8]_min     Voltage min value.
  77                 Unit: millivolt
  78                 Read/Write
  79
  80 in[0-8]_max     Voltage max value.
  81                 Unit: millivolt
  82                 Read/Write
  83
  84 in[0-8]_input   Voltage input value.
  85                 Unit: millivolt
  86                 Read only
  87                 Actual voltage depends on the scaling resistors on the
  88                 motherboard, as recommended in the chip datasheet.
  89                 This varies by chip and by motherboard.
  90                 Because of this variation, values are generally NOT scaled
  91                 by the chip driver, and must be done by the application.
  92                 However, some drivers (notably lm87 and via686a)
  93                 do scale, with various degrees of success.
  94                 These drivers will output the actual voltage.
  95
  96                 Typical usage:
  97                         in0_*   CPU #1 voltage (not scaled)
  98                         in1_*   CPU #2 voltage (not scaled)
  99                         in2_*   3.3V nominal (not scaled)
 100                         in3_*   5.0V nominal (scaled)
 101                         in4_*   12.0V nominal (scaled)
 102                         in5_*   -12.0V nominal (scaled)
 103                         in6_*   -5.0V nominal (scaled)
 104                         in7_*   varies
 105                         in8_*   varies
 106
 107 cpu[0-1]_vid    CPU core reference voltage.
 108                 Unit: millivolt
 109                 Read only.
 110                 Not always correct.
 111
 112 vrm             Voltage Regulator Module version number.
 113                 Read only.
 114                 Two digit number, first is major version, second is
 115                 minor version.
 116                 Affects the way the driver calculates the CPU core reference
 117                 voltage from the vid pins.
 118
 119
 120 ********
 121 * Fans *
 122 ********
 123
 124 fan[1-3]_min    Fan minimum value
 125                 Unit: revolution/min (RPM)
 126                 Read/Write.
 127
 128 fan[1-3]_input  Fan input value.
 129                 Unit: revolution/min (RPM)
 130                 Read only.
 131
 132 fan[1-3]_div    Fan divisor.
 133                 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
 134                 Some chips only support values 1, 2, 4 and 8.
 135                 Note that this is actually an internal clock divisor, which
 136                 affects the measurable speed range, not the read value.
 137
 138 *******
 139 * PWM *
 140 *******
 141
 142 pwm[1-3]        Pulse width modulation fan control.
 143                 Integer value in the range 0 to 255
 144                 Read/Write
 145                 255 is max or 100%.
 146
 147 pwm[1-3]_enable
 148                 Switch PWM on and off.
 149                 Not always present even if fan*_pwm is.
 150                 0 to turn off
 151                 1 to turn on in manual mode
 152                 2 to turn on in automatic mode
 153                 Read/Write
 154
 155 pwm[1-*]_auto_channels_temp
 156                 Select which temperature channels affect this PWM output in
 157                 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
 158                 Which values are possible depend on the chip used.
 159
 160 pwm[1-*]_auto_point[1-*]_pwm
 161 pwm[1-*]_auto_point[1-*]_temp
 162 pwm[1-*]_auto_point[1-*]_temp_hyst
 163                 Define the PWM vs temperature curve. Number of trip points is
 164                 chip-dependent. Use this for chips which associate trip points
 165                 to PWM output channels.
 166
 167 OR
 168
 169 temp[1-*]_auto_point[1-*]_pwm
 170 temp[1-*]_auto_point[1-*]_temp
 171 temp[1-*]_auto_point[1-*]_temp_hyst
 172                 Define the PWM vs temperature curve. Number of trip points is
 173                 chip-dependent. Use this for chips which associate trip points
 174                 to temperature channels.
 175
 176
 177 ****************
 178 * Temperatures *
 179 ****************
 180
 181 temp[1-3]_type  Sensor type selection.
 182                 Integers 1, 2, 3 or thermistor Beta value (3435)
 183                 Read/Write.
 184                 1: PII/Celeron Diode
 185                 2: 3904 transistor
 186                 3: thermal diode
 187                 Not all types are supported by all chips
 188
 189 temp[1-4]_max   Temperature max value.
 190                 Unit: millidegree Celcius
 191                 Read/Write value.
 192
 193 temp[1-3]_min   Temperature min value.
 194                 Unit: millidegree Celcius
 195                 Read/Write value.
 196
 197 temp[1-3]_max_hyst
 198                 Temperature hysteresis value for max limit.
 199                 Unit: millidegree Celcius
 200                 Must be reported as an absolute temperature, NOT a delta
 201                 from the max value.
 202                 Read/Write value.
 203
 204 temp[1-4]_input Temperature input value.
 205                 Unit: millidegree Celcius
 206                 Read only value.
 207
 208 temp[1-4]_crit  Temperature critical value, typically greater than
 209                 corresponding temp_max values.
 210                 Unit: millidegree Celcius
 211                 Read/Write value.
 212
 213 temp[1-2]_crit_hyst
 214                 Temperature hysteresis value for critical limit.
 215                 Unit: millidegree Celcius
 216                 Must be reported as an absolute temperature, NOT a delta
 217                 from the critical value.
 218                 Read/Write value.
 219
 220                 If there are multiple temperature sensors, temp1_* is
 221                 generally the sensor inside the chip itself,
 222                 reported as "motherboard temperature".  temp2_* to
 223                 temp4_* are generally sensors external to the chip
 224                 itself, for example the thermal diode inside the CPU or
 225                 a thermistor nearby.
 226
 227
 228 ************
 229 * Currents *
 230 ************
 231
 232 Note that no known chip provides current measurements as of writing,
 233 so this part is theoretical, so to say.
 234
 235 curr[1-n]_max   Current max value
 236                 Unit: milliampere
 237                 Read/Write.
 238
 239 curr[1-n]_min   Current min value.
 240                 Unit: milliampere
 241                 Read/Write.
 242
 243 curr[1-n]_input Current input value
 244                 Unit: milliampere
 245                 Read only.
 246
 247
 248 *********
 249 * Other *
 250 *********
 251
 252 alarms          Alarm bitmask.
 253                 Read only.
 254                 Integer representation of one to four bytes.
 255                 A '1' bit means an alarm.
 256                 Chips should be programmed for 'comparator' mode so that
 257                 the alarm will 'come back' after you read the register
 258                 if it is still valid.
 259                 Generally a direct representation of a chip's internal
 260                 alarm registers; there is no standard for the position
 261                 of individual bits.
 262                 Bits are defined in kernel/include/sensors.h.
 263
 264 beep_enable     Beep/interrupt enable
 265                 0 to disable.
 266                 1 to enable.
 267                 Read/Write
 268
 269 beep_mask       Bitmask for beep.
 270                 Same format as 'alarms' with the same bit locations.
 271                 Read/Write
 272
 273 eeprom          Raw EEPROM data in binary form.
 274                 Read only.