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+Naming and data format standards for sysfs files
+------------------------------------------------
+
+The libsensors library offers an interface to the raw sensors data
+through the sysfs interface. Since lm-sensors 3.0.0, libsensors is
+completely chip-independent. It assumes that all the kernel drivers
+implement the standard sysfs interface described in this document.
+This makes adding or updating support for any given chip very easy, as
+libsensors, and applications using it, do not need to be modified.
+This is a major improvement compared to lm-sensors 2.
+
+Note that motherboards vary widely in the connections to sensor chips.
+There is no standard that ensures, for example, that the second
+temperature sensor is connected to the CPU, or that the second fan is on
+the CPU. Also, some values reported by the chips need some computation
+before they make full sense. For example, most chips can only measure
+voltages between 0 and +4V. Other voltages are scaled back into that
+range using external resistors. Since the values of these resistors
+can change from motherboard to motherboard, the conversions cannot be
+hard coded into the driver and have to be done in user space.
+
+For this reason, even if we aim at a chip-independent libsensors, it will
+still require a configuration file (e.g. /etc/sensors.conf) for proper
+values conversion, labeling of inputs and hiding of unused inputs.
+
+An alternative method that some programs use is to access the sysfs
+files directly. This document briefly describes the standards that the
+drivers follow, so that an application program can scan for entries and
+access this data in a simple and consistent way. That said, such programs
+will have to implement conversion, labeling and hiding of inputs. For
+this reason, it is still not recommended to bypass the library.
+
+Each chip gets its own directory in the sysfs /sys/devices tree. To
+find all sensor chips, it is easier to follow the device symlinks from
+/sys/class/hwmon/hwmon*.
+
+Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
+in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
+in the hwmon "class" device directory are also supported. Complex drivers
+(e.g. drivers for multifunction chips) may want to use this possibility to
+avoid namespace pollution. The only drawback will be that older versions of
+libsensors won't support the driver in question.
+
+All sysfs values are fixed point numbers.
+
+There is only one value per file, unlike the older /proc specification.
+The common scheme for files naming is: <type><number>_<item>. Usual
+types for sensor chips are "in" (voltage), "temp" (temperature) and
+"fan" (fan). Usual items are "input" (measured value), "max" (high
+threshold, "min" (low threshold). Numbering usually starts from 1,
+except for voltages which start from 0 (because most data sheets use
+this). A number is always used for elements that can be present more
+than once, even if there is a single element of the given type on the
+specific chip. Other files do not refer to a specific element, so
+they have a simple name, and no number.
+
+Alarms are direct indications read from the chips. The drivers do NOT
+make comparisons of readings to thresholds. This allows violations
+between readings to be caught and alarmed. The exact definition of an
+alarm (for example, whether a threshold must be met or must be exceeded
+to cause an alarm) is chip-dependent.
+
+When setting values of hwmon sysfs attributes, the string representation of
+the desired value must be written, note that strings which are not a number
+are interpreted as 0! For more on how written strings are interpreted see the
+"sysfs attribute writes interpretation" section at the end of this file.
+
+-------------------------------------------------------------------------
+
+[0-*] denotes any positive number starting from 0
+[1-*] denotes any positive number starting from 1
+RO read only value
+WO write only value
+RW read/write value
+
+Read/write values may be read-only for some chips, depending on the
+hardware implementation.
+
+All entries (except name) are optional, and should only be created in a
+given driver if the chip has the feature.
+
+
+*********************
+* Global attributes *
+*********************
+
+name The chip name.
+ This should be a short, lowercase string, not containing
+ spaces nor dashes, representing the chip name. This is
+ the only mandatory attribute.
+ I2C devices get this attribute created automatically.
+ RO
+
+update_interval The interval at which the chip will update readings.
+ Unit: millisecond
+ RW
+ Some devices have a variable update rate or interval.
+ This attribute can be used to change it to the desired value.
+
+
+************
+* Voltages *
+************
+
+in[0-*]_min Voltage min value.
+ Unit: millivolt
+ RW
+
+in[0-*]_lcrit Voltage critical min value.
+ Unit: millivolt
+ RW
+ If voltage drops to or below this limit, the system may
+ take drastic action such as power down or reset. At the very
+ least, it should report a fault.
+
+in[0-*]_max Voltage max value.
+ Unit: millivolt
+ RW
+
+in[0-*]_crit Voltage critical max value.
+ Unit: millivolt
+ RW
+ If voltage reaches or exceeds this limit, the system may
+ take drastic action such as power down or reset. At the very
+ least, it should report a fault.
+
+in[0-*]_input Voltage input value.
+ Unit: millivolt
+ RO
+ Voltage measured on the chip pin.
+ Actual voltage depends on the scaling resistors on the
+ motherboard, as recommended in the chip datasheet.
+ This varies by chip and by motherboard.
+ Because of this variation, values are generally NOT scaled
+ by the chip driver, and must be done by the application.
+ However, some drivers (notably lm87 and via686a)
+ do scale, because of internal resistors built into a chip.
+ These drivers will output the actual voltage. Rule of
+ thumb: drivers should report the voltage values at the
+ "pins" of the chip.
+
+in[0-*]_average
+ Average voltage
+ Unit: millivolt
+ RO
+
+in[0-*]_lowest
+ Historical minimum voltage
+ Unit: millivolt
+ RO
+
+in[0-*]_highest
+ Historical maximum voltage
+ Unit: millivolt
+ RO
+
+in[0-*]_reset_history
+ Reset inX_lowest and inX_highest
+ WO
+
+in_reset_history
+ Reset inX_lowest and inX_highest for all sensors
+ WO
+
+in[0-*]_label Suggested voltage channel label.
+ Text string
+ Should only be created if the driver has hints about what
+ this voltage channel is being used for, and user-space
+ doesn't. In all other cases, the label is provided by
+ user-space.
+ RO
+
+cpu[0-*]_vid CPU core reference voltage.
+ Unit: millivolt
+ RO
+ Not always correct.
+
+vrm Voltage Regulator Module version number.
+ RW (but changing it should no more be necessary)
+ Originally the VRM standard version multiplied by 10, but now
+ an arbitrary number, as not all standards have a version
+ number.
+ Affects the way the driver calculates the CPU core reference
+ voltage from the vid pins.
+
+Also see the Alarms section for status flags associated with voltages.
+
+
+********
+* Fans *
+********
+
+fan[1-*]_min Fan minimum value
+ Unit: revolution/min (RPM)
+ RW
+
+fan[1-*]_max Fan maximum value
+ Unit: revolution/min (RPM)
+ Only rarely supported by the hardware.
+ RW
+
+fan[1-*]_input Fan input value.
+ Unit: revolution/min (RPM)
+ RO
+
+fan[1-*]_div Fan divisor.
+ Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
+ RW
+ Some chips only support values 1, 2, 4 and 8.
+ Note that this is actually an internal clock divisor, which
+ affects the measurable speed range, not the read value.
+
+fan[1-*]_pulses Number of tachometer pulses per fan revolution.
+ Integer value, typically between 1 and 4.
+ RW
+ This value is a characteristic of the fan connected to the
+ device's input, so it has to be set in accordance with the fan
+ model.
+ Should only be created if the chip has a register to configure
+ the number of pulses. In the absence of such a register (and
+ thus attribute) the value assumed by all devices is 2 pulses
+ per fan revolution.
+
+fan[1-*]_target
+ Desired fan speed
+ Unit: revolution/min (RPM)
+ RW
+ Only makes sense if the chip supports closed-loop fan speed
+ control based on the measured fan speed.
+
+fan[1-*]_label Suggested fan channel label.
+ Text string
+ Should only be created if the driver has hints about what
+ this fan channel is being used for, and user-space doesn't.
+ In all other cases, the label is provided by user-space.
+ RO
+
+Also see the Alarms section for status flags associated with fans.
+
+
+*******
+* PWM *
+*******
+
+pwm[1-*] Pulse width modulation fan control.
+ Integer value in the range 0 to 255
+ RW
+ 255 is max or 100%.
+
+pwm[1-*]_enable
+ Fan speed control method:
+ 0: no fan speed control (i.e. fan at full speed)
+ 1: manual fan speed control enabled (using pwm[1-*])
+ 2+: automatic fan speed control enabled
+ Check individual chip documentation files for automatic mode
+ details.
+ RW
+
+pwm[1-*]_mode 0: DC mode (direct current)
+ 1: PWM mode (pulse-width modulation)
+ RW
+
+pwm[1-*]_freq Base PWM frequency in Hz.
+ Only possibly available when pwmN_mode is PWM, but not always
+ present even then.
+ RW
+
+pwm[1-*]_auto_channels_temp
+ Select which temperature channels affect this PWM output in
+ auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
+ Which values are possible depend on the chip used.
+ RW
+
+pwm[1-*]_auto_point[1-*]_pwm
+pwm[1-*]_auto_point[1-*]_temp
+pwm[1-*]_auto_point[1-*]_temp_hyst
+ Define the PWM vs temperature curve. Number of trip points is
+ chip-dependent. Use this for chips which associate trip points
+ to PWM output channels.
+ RW
+
+temp[1-*]_auto_point[1-*]_pwm
+temp[1-*]_auto_point[1-*]_temp
+temp[1-*]_auto_point[1-*]_temp_hyst
+ Define the PWM vs temperature curve. Number of trip points is
+ chip-dependent. Use this for chips which associate trip points
+ to temperature channels.
+ RW
+
+There is a third case where trip points are associated to both PWM output
+channels and temperature channels: the PWM values are associated to PWM
+output channels while the temperature values are associated to temperature
+channels. In that case, the result is determined by the mapping between
+temperature inputs and PWM outputs. When several temperature inputs are
+mapped to a given PWM output, this leads to several candidate PWM values.
+The actual result is up to the chip, but in general the highest candidate
+value (fastest fan speed) wins.
+
+
+****************
+* Temperatures *
+****************
+
+temp[1-*]_type Sensor type selection.
+ Integers 1 to 6
+ RW
+ 1: CPU embedded diode
+ 2: 3904 transistor
+ 3: thermal diode
+ 4: thermistor
+ 5: AMD AMDSI
+ 6: Intel PECI
+ Not all types are supported by all chips
+
+temp[1-*]_max Temperature max value.
+ Unit: millidegree Celsius (or millivolt, see below)
+ RW
+
+temp[1-*]_min Temperature min value.
+ Unit: millidegree Celsius
+ RW
+
+temp[1-*]_max_hyst
+ Temperature hysteresis value for max limit.
+ Unit: millidegree Celsius
+ Must be reported as an absolute temperature, NOT a delta
+ from the max value.
+ RW
+
+temp[1-*]_input Temperature input value.
+ Unit: millidegree Celsius
+ RO
+
+temp[1-*]_crit Temperature critical max value, typically greater than
+ corresponding temp_max values.
+ Unit: millidegree Celsius
+ RW
+
+temp[1-*]_crit_hyst
+ Temperature hysteresis value for critical limit.
+ Unit: millidegree Celsius
+ Must be reported as an absolute temperature, NOT a delta
+ from the critical value.
+ RW
+
+temp[1-*]_emergency
+ Temperature emergency max value, for chips supporting more than
+ two upper temperature limits. Must be equal or greater than
+ corresponding temp_crit values.
+ Unit: millidegree Celsius
+ RW
+
+temp[1-*]_emergency_hyst
+ Temperature hysteresis value for emergency limit.
+ Unit: millidegree Celsius
+ Must be reported as an absolute temperature, NOT a delta
+ from the emergency value.
+ RW
+
+temp[1-*]_lcrit Temperature critical min value, typically lower than
+ corresponding temp_min values.
+ Unit: millidegree Celsius
+ RW
+
+temp[1-*]_offset
+ Temperature offset which is added to the temperature reading
+ by the chip.
+ Unit: millidegree Celsius
+ Read/Write value.
+
+temp[1-*]_label Suggested temperature channel label.
+ Text string
+ Should only be created if the driver has hints about what
+ this temperature channel is being used for, and user-space
+ doesn't. In all other cases, the label is provided by
+ user-space.
+ RO
+
+temp[1-*]_lowest
+ Historical minimum temperature
+ Unit: millidegree Celsius
+ RO
+
+temp[1-*]_highest
+ Historical maximum temperature
+ Unit: millidegree Celsius
+ RO
+
+temp[1-*]_reset_history
+ Reset temp_lowest and temp_highest
+ WO
+
+temp_reset_history
+ Reset temp_lowest and temp_highest for all sensors
+ WO
+
+Some chips measure temperature using external thermistors and an ADC, and
+report the temperature measurement as a voltage. Converting this voltage
+back to a temperature (or the other way around for limits) requires
+mathematical functions not available in the kernel, so the conversion
+must occur in user space. For these chips, all temp* files described
+above should contain values expressed in millivolt instead of millidegree
+Celsius. In other words, such temperature channels are handled as voltage
+channels by the driver.
+
+Also see the Alarms section for status flags associated with temperatures.
+
+
+************
+* Currents *
+************
+
+curr[1-*]_max Current max value
+ Unit: milliampere
+ RW
+
+curr[1-*]_min Current min value.
+ Unit: milliampere
+ RW
+
+curr[1-*]_lcrit Current critical low value
+ Unit: milliampere
+ RW
+
+curr[1-*]_crit Current critical high value.
+ Unit: milliampere
+ RW
+
+curr[1-*]_input Current input value
+ Unit: milliampere
+ RO
+
+curr[1-*]_average
+ Average current use
+ Unit: milliampere
+ RO
+
+curr[1-*]_lowest
+ Historical minimum current
+ Unit: milliampere
+ RO
+
+curr[1-*]_highest
+ Historical maximum current
+ Unit: milliampere
+ RO
+
+curr[1-*]_reset_history
+ Reset currX_lowest and currX_highest
+ WO
+
+curr_reset_history
+ Reset currX_lowest and currX_highest for all sensors
+ WO
+
+Also see the Alarms section for status flags associated with currents.
+
+*********
+* Power *
+*********
+
+power[1-*]_average Average power use
+ Unit: microWatt
+ RO
+
+power[1-*]_average_interval Power use averaging interval. A poll
+ notification is sent to this file if the
+ hardware changes the averaging interval.
+ Unit: milliseconds
+ RW
+
+power[1-*]_average_interval_max Maximum power use averaging interval
+ Unit: milliseconds
+ RO
+
+power[1-*]_average_interval_min Minimum power use averaging interval
+ Unit: milliseconds
+ RO
+
+power[1-*]_average_highest Historical average maximum power use
+ Unit: microWatt
+ RO
+
+power[1-*]_average_lowest Historical average minimum power use
+ Unit: microWatt
+ RO
+
+power[1-*]_average_max A poll notification is sent to
+ power[1-*]_average when power use
+ rises above this value.
+ Unit: microWatt
+ RW
+
+power[1-*]_average_min A poll notification is sent to
+ power[1-*]_average when power use
+ sinks below this value.
+ Unit: microWatt
+ RW
+
+power[1-*]_input Instantaneous power use
+ Unit: microWatt
+ RO
+
+power[1-*]_input_highest Historical maximum power use
+ Unit: microWatt
+ RO
+
+power[1-*]_input_lowest Historical minimum power use
+ Unit: microWatt
+ RO
+
+power[1-*]_reset_history Reset input_highest, input_lowest,
+ average_highest and average_lowest.
+ WO
+
+power[1-*]_accuracy Accuracy of the power meter.
+ Unit: Percent
+ RO
+
+power[1-*]_cap If power use rises above this limit, the
+ system should take action to reduce power use.
+ A poll notification is sent to this file if the
+ cap is changed by the hardware. The *_cap
+ files only appear if the cap is known to be
+ enforced by hardware.
+ Unit: microWatt
+ RW
+
+power[1-*]_cap_hyst Margin of hysteresis built around capping and
+ notification.
+ Unit: microWatt
+ RW
+
+power[1-*]_cap_max Maximum cap that can be set.
+ Unit: microWatt
+ RO
+
+power[1-*]_cap_min Minimum cap that can be set.
+ Unit: microWatt
+ RO
+
+power[1-*]_max Maximum power.
+ Unit: microWatt
+ RW
+
+power[1-*]_crit Critical maximum power.
+ If power rises to or above this limit, the
+ system is expected take drastic action to reduce
+ power consumption, such as a system shutdown or
+ a forced powerdown of some devices.
+ Unit: microWatt
+ RW
+
+Also see the Alarms section for status flags associated with power readings.
+
+**********
+* Energy *
+**********
+
+energy[1-*]_input Cumulative energy use
+ Unit: microJoule
+ RO
+
+
+************
+* Humidity *
+************
+
+humidity[1-*]_input Humidity
+ Unit: milli-percent (per cent mille, pcm)
+ RO
+
+
+**********
+* Alarms *
+**********
+
+Each channel or limit may have an associated alarm file, containing a
+boolean value. 1 means than an alarm condition exists, 0 means no alarm.
+
+Usually a given chip will either use channel-related alarms, or
+limit-related alarms, not both. The driver should just reflect the hardware
+implementation.
+
+in[0-*]_alarm
+curr[1-*]_alarm
+power[1-*]_alarm
+fan[1-*]_alarm
+temp[1-*]_alarm
+ Channel alarm
+ 0: no alarm
+ 1: alarm
+ RO
+
+OR
+
+in[0-*]_min_alarm
+in[0-*]_max_alarm
+in[0-*]_lcrit_alarm
+in[0-*]_crit_alarm
+curr[1-*]_min_alarm
+curr[1-*]_max_alarm
+curr[1-*]_lcrit_alarm
+curr[1-*]_crit_alarm
+power[1-*]_cap_alarm
+power[1-*]_max_alarm
+power[1-*]_crit_alarm
+fan[1-*]_min_alarm
+fan[1-*]_max_alarm
+temp[1-*]_min_alarm
+temp[1-*]_max_alarm
+temp[1-*]_lcrit_alarm
+temp[1-*]_crit_alarm
+temp[1-*]_emergency_alarm
+ Limit alarm
+ 0: no alarm
+ 1: alarm
+ RO
+
+Each input channel may have an associated fault file. This can be used
+to notify open diodes, unconnected fans etc. where the hardware
+supports it. When this boolean has value 1, the measurement for that
+channel should not be trusted.
+
+fan[1-*]_fault
+temp[1-*]_fault
+ Input fault condition
+ 0: no fault occurred
+ 1: fault condition
+ RO
+
+Some chips also offer the possibility to get beeped when an alarm occurs:
+
+beep_enable Master beep enable
+ 0: no beeps
+ 1: beeps
+ RW
+
+in[0-*]_beep
+curr[1-*]_beep
+fan[1-*]_beep
+temp[1-*]_beep
+ Channel beep
+ 0: disable
+ 1: enable
+ RW
+
+In theory, a chip could provide per-limit beep masking, but no such chip
+was seen so far.
+
+Old drivers provided a different, non-standard interface to alarms and
+beeps. These interface files are deprecated, but will be kept around
+for compatibility reasons:
+
+alarms Alarm bitmask.
+ RO
+ Integer representation of one to four bytes.
+ A '1' bit means an alarm.
+ Chips should be programmed for 'comparator' mode so that
+ the alarm will 'come back' after you read the register
+ if it is still valid.
+ Generally a direct representation of a chip's internal
+ alarm registers; there is no standard for the position
+ of individual bits. For this reason, the use of this
+ interface file for new drivers is discouraged. Use
+ individual *_alarm and *_fault files instead.
+ Bits are defined in kernel/include/sensors.h.
+
+beep_mask Bitmask for beep.
+ Same format as 'alarms' with the same bit locations,
+ use discouraged for the same reason. Use individual
+ *_beep files instead.
+ RW
+
+
+***********************
+* Intrusion detection *
+***********************
+
+intrusion[0-*]_alarm
+ Chassis intrusion detection
+ 0: OK
+ 1: intrusion detected
+ RW
+ Contrary to regular alarm flags which clear themselves
+ automatically when read, this one sticks until cleared by
+ the user. This is done by writing 0 to the file. Writing
+ other values is unsupported.
+
+intrusion[0-*]_beep
+ Chassis intrusion beep
+ 0: disable
+ 1: enable
+ RW
+
+
+sysfs attribute writes interpretation
+-------------------------------------
+
+hwmon sysfs attributes always contain numbers, so the first thing to do is to
+convert the input to a number, there are 2 ways todo this depending whether
+the number can be negative or not:
+unsigned long u = simple_strtoul(buf, NULL, 10);
+long s = simple_strtol(buf, NULL, 10);
+
+With buf being the buffer with the user input being passed by the kernel.
+Notice that we do not use the second argument of strto[u]l, and thus cannot
+tell when 0 is returned, if this was really 0 or is caused by invalid input.
+This is done deliberately as checking this everywhere would add a lot of
+code to the kernel.
+
+Notice that it is important to always store the converted value in an
+unsigned long or long, so that no wrap around can happen before any further
+checking.
+
+After the input string is converted to an (unsigned) long, the value should be
+checked if its acceptable. Be careful with further conversions on the value
+before checking it for validity, as these conversions could still cause a wrap
+around before the check. For example do not multiply the result, and only
+add/subtract if it has been divided before the add/subtract.
+
+What to do if a value is found to be invalid, depends on the type of the
+sysfs attribute that is being set. If it is a continuous setting like a
+tempX_max or inX_max attribute, then the value should be clamped to its
+limits using clamp_val(value, min_limit, max_limit). If it is not continuous
+like for example a tempX_type, then when an invalid value is written,
+-EINVAL should be returned.
+
+Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
+
+ long v = simple_strtol(buf, NULL, 10) / 1000;
+ v = clamp_val(v, -128, 127);
+ /* write v to register */
+
+Example2, fan divider setting, valid values 2, 4 and 8:
+
+ unsigned long v = simple_strtoul(buf, NULL, 10);
+
+ switch (v) {
+ case 2: v = 1; break;
+ case 4: v = 2; break;
+ case 8: v = 3; break;
+ default:
+ return -EINVAL;
+ }
+ /* write v to register */