657 lines
18 KiB
ReStructuredText
657 lines
18 KiB
ReStructuredText
Naming and data format standards for sysfs files
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================================================
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The libsensors library offers an interface to the raw sensors data
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through the sysfs interface. Since lm-sensors 3.0.0, libsensors is
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completely chip-independent. It assumes that all the kernel drivers
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implement the standard sysfs interface described in this document.
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This makes adding or updating support for any given chip very easy, as
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libsensors, and applications using it, do not need to be modified.
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This is a major improvement compared to lm-sensors 2.
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Note that motherboards vary widely in the connections to sensor chips.
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There is no standard that ensures, for example, that the second
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temperature sensor is connected to the CPU, or that the second fan is on
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the CPU. Also, some values reported by the chips need some computation
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before they make full sense. For example, most chips can only measure
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voltages between 0 and +4V. Other voltages are scaled back into that
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range using external resistors. Since the values of these resistors
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can change from motherboard to motherboard, the conversions cannot be
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hard coded into the driver and have to be done in user space.
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For this reason, even if we aim at a chip-independent libsensors, it will
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still require a configuration file (e.g. /etc/sensors.conf) for proper
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values conversion, labeling of inputs and hiding of unused inputs.
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An alternative method that some programs use is to access the sysfs
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files directly. This document briefly describes the standards that the
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drivers follow, so that an application program can scan for entries and
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access this data in a simple and consistent way. That said, such programs
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will have to implement conversion, labeling and hiding of inputs. For
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this reason, it is still not recommended to bypass the library.
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Each chip gets its own directory in the sysfs /sys/devices tree. To
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find all sensor chips, it is easier to follow the device symlinks from
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`/sys/class/hwmon/hwmon*`.
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Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
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in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
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in the hwmon "class" device directory are also supported. Complex drivers
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(e.g. drivers for multifunction chips) may want to use this possibility to
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avoid namespace pollution. The only drawback will be that older versions of
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libsensors won't support the driver in question.
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All sysfs values are fixed point numbers.
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There is only one value per file, unlike the older /proc specification.
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The common scheme for files naming is: <type><number>_<item>. Usual
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types for sensor chips are "in" (voltage), "temp" (temperature) and
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"fan" (fan). Usual items are "input" (measured value), "max" (high
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threshold, "min" (low threshold). Numbering usually starts from 1,
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except for voltages which start from 0 (because most data sheets use
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this). A number is always used for elements that can be present more
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than once, even if there is a single element of the given type on the
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specific chip. Other files do not refer to a specific element, so
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they have a simple name, and no number.
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Alarms are direct indications read from the chips. The drivers do NOT
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make comparisons of readings to thresholds. This allows violations
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between readings to be caught and alarmed. The exact definition of an
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alarm (for example, whether a threshold must be met or must be exceeded
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to cause an alarm) is chip-dependent.
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When setting values of hwmon sysfs attributes, the string representation of
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the desired value must be written, note that strings which are not a number
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are interpreted as 0! For more on how written strings are interpreted see the
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"sysfs attribute writes interpretation" section at the end of this file.
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Attribute access
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----------------
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Hardware monitoring sysfs attributes are displayed by unrestricted userspace
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applications. For this reason, all standard ABI attributes shall be world
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readable. Writeable standard ABI attributes shall be writeable only for
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privileged users.
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-------------------------------------------------------------------------
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======= ===========================================
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`[0-*]` denotes any positive number starting from 0
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`[1-*]` denotes any positive number starting from 1
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RO read only value
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WO write only value
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RW read/write value
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======= ===========================================
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Read/write values may be read-only for some chips, depending on the
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hardware implementation.
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All entries (except name) are optional, and should only be created in a
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given driver if the chip has the feature.
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See Documentation/ABI/testing/sysfs-class-hwmon for a complete description
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of the attributes.
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*****************
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Global attributes
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*****************
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`name`
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The chip name.
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`label`
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A descriptive label that allows to uniquely identify a device
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within the system.
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`update_interval`
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The interval at which the chip will update readings.
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********
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Voltages
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********
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`in[0-*]_min`
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Voltage min value.
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`in[0-*]_lcrit`
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Voltage critical min value.
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`in[0-*]_max`
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Voltage max value.
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`in[0-*]_crit`
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Voltage critical max value.
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`in[0-*]_input`
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Voltage input value.
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`in[0-*]_average`
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Average voltage
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`in[0-*]_lowest`
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Historical minimum voltage
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`in[0-*]_highest`
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Historical maximum voltage
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`in[0-*]_reset_history`
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Reset inX_lowest and inX_highest
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`in_reset_history`
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Reset inX_lowest and inX_highest for all sensors
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`in[0-*]_label`
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Suggested voltage channel label.
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`in[0-*]_enable`
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Enable or disable the sensors.
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`cpu[0-*]_vid`
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CPU core reference voltage.
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`vrm`
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Voltage Regulator Module version number.
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`in[0-*]_rated_min`
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Minimum rated voltage.
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`in[0-*]_rated_max`
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Maximum rated voltage.
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Also see the Alarms section for status flags associated with voltages.
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****
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Fans
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****
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`fan[1-*]_min`
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Fan minimum value
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`fan[1-*]_max`
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Fan maximum value
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`fan[1-*]_input`
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Fan input value.
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`fan[1-*]_div`
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Fan divisor.
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`fan[1-*]_pulses`
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Number of tachometer pulses per fan revolution.
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`fan[1-*]_target`
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Desired fan speed
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`fan[1-*]_label`
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Suggested fan channel label.
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`fan[1-*]_enable`
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Enable or disable the sensors.
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Also see the Alarms section for status flags associated with fans.
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***
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PWM
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***
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`pwm[1-*]`
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Pulse width modulation fan control.
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`pwm[1-*]_enable`
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Fan speed control method:
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`pwm[1-*]_mode`
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direct current or pulse-width modulation.
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`pwm[1-*]_freq`
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Base PWM frequency in Hz.
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`pwm[1-*]_auto_channels_temp`
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Select which temperature channels affect this PWM output in
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auto mode.
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`pwm[1-*]_auto_point[1-*]_pwm` / `pwm[1-*]_auto_point[1-*]_temp` / `pwm[1-*]_auto_point[1-*]_temp_hyst`
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Define the PWM vs temperature curve.
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`temp[1-*]_auto_point[1-*]_pwm` / `temp[1-*]_auto_point[1-*]_temp` / `temp[1-*]_auto_point[1-*]_temp_hyst`
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Define the PWM vs temperature curve.
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There is a third case where trip points are associated to both PWM output
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channels and temperature channels: the PWM values are associated to PWM
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output channels while the temperature values are associated to temperature
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channels. In that case, the result is determined by the mapping between
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temperature inputs and PWM outputs. When several temperature inputs are
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mapped to a given PWM output, this leads to several candidate PWM values.
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The actual result is up to the chip, but in general the highest candidate
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value (fastest fan speed) wins.
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************
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Temperatures
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************
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`temp[1-*]_type`
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Sensor type selection.
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`temp[1-*]_max`
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Temperature max value.
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`temp[1-*]_min`
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Temperature min value.
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`temp[1-*]_max_hyst`
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Temperature hysteresis value for max limit.
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`temp[1-*]_min_hyst`
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Temperature hysteresis value for min limit.
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`temp[1-*]_input`
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Temperature input value.
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`temp[1-*]_crit`
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Temperature critical max value, typically greater than
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corresponding temp_max values.
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`temp[1-*]_crit_hyst`
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Temperature hysteresis value for critical limit.
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`temp[1-*]_emergency`
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Temperature emergency max value, for chips supporting more than
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two upper temperature limits.
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`temp[1-*]_emergency_hyst`
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Temperature hysteresis value for emergency limit.
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`temp[1-*]_lcrit`
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Temperature critical min value, typically lower than
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corresponding temp_min values.
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`temp[1-*]_lcrit_hyst`
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Temperature hysteresis value for critical min limit.
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`temp[1-*]_offset`
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Temperature offset which is added to the temperature reading
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by the chip.
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`temp[1-*]_label`
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Suggested temperature channel label.
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`temp[1-*]_lowest`
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Historical minimum temperature
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`temp[1-*]_highest`
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Historical maximum temperature
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`temp[1-*]_reset_history`
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Reset temp_lowest and temp_highest
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`temp_reset_history`
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Reset temp_lowest and temp_highest for all sensors
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`temp[1-*]_enable`
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Enable or disable the sensors.
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`temp[1-*]_rated_min`
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Minimum rated temperature.
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`temp[1-*]_rated_max`
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Maximum rated temperature.
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Some chips measure temperature using external thermistors and an ADC, and
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report the temperature measurement as a voltage. Converting this voltage
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back to a temperature (or the other way around for limits) requires
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mathematical functions not available in the kernel, so the conversion
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must occur in user space. For these chips, all temp* files described
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above should contain values expressed in millivolt instead of millidegree
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Celsius. In other words, such temperature channels are handled as voltage
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channels by the driver.
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Also see the Alarms section for status flags associated with temperatures.
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********
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Currents
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********
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`curr[1-*]_max`
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Current max value.
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`curr[1-*]_min`
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Current min value.
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`curr[1-*]_lcrit`
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Current critical low value
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`curr[1-*]_crit`
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Current critical high value.
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`curr[1-*]_input`
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Current input value.
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`curr[1-*]_average`
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Average current use.
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`curr[1-*]_lowest`
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Historical minimum current.
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`curr[1-*]_highest`
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Historical maximum current.
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`curr[1-*]_reset_history`
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Reset currX_lowest and currX_highest
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WO
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`curr_reset_history`
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Reset currX_lowest and currX_highest for all sensors.
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`curr[1-*]_enable`
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Enable or disable the sensors.
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`curr[1-*]_rated_min`
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Minimum rated current.
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`curr[1-*]_rated_max`
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Maximum rated current.
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Also see the Alarms section for status flags associated with currents.
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*****
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Power
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*****
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`power[1-*]_average`
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Average power use.
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`power[1-*]_average_interval`
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Power use averaging interval.
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`power[1-*]_average_interval_max`
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Maximum power use averaging interval.
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`power[1-*]_average_interval_min`
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Minimum power use averaging interval.
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`power[1-*]_average_highest`
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Historical average maximum power use
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`power[1-*]_average_lowest`
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Historical average minimum power use
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`power[1-*]_average_max`
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A poll notification is sent to `power[1-*]_average` when
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power use rises above this value.
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`power[1-*]_average_min`
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A poll notification is sent to `power[1-*]_average` when
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power use sinks below this value.
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`power[1-*]_input`
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Instantaneous power use.
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`power[1-*]_input_highest`
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Historical maximum power use
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`power[1-*]_input_lowest`
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Historical minimum power use.
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`power[1-*]_reset_history`
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Reset input_highest, input_lowest, average_highest and
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average_lowest.
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`power[1-*]_accuracy`
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Accuracy of the power meter.
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`power[1-*]_cap`
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If power use rises above this limit, the
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system should take action to reduce power use.
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`power[1-*]_cap_hyst`
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Margin of hysteresis built around capping and notification.
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`power[1-*]_cap_max`
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Maximum cap that can be set.
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`power[1-*]_cap_min`
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Minimum cap that can be set.
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`power[1-*]_max`
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Maximum power.
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`power[1-*]_crit`
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Critical maximum power.
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If power rises to or above this limit, the
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system is expected take drastic action to reduce
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power consumption, such as a system shutdown or
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a forced powerdown of some devices.
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Unit: microWatt
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RW
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`power[1-*]_enable`
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Enable or disable the sensors.
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When disabled the sensor read will return
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-ENODATA.
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- 1: Enable
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- 0: Disable
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RW
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`power[1-*]_rated_min`
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Minimum rated power.
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Unit: microWatt
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RO
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`power[1-*]_rated_max`
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Maximum rated power.
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Unit: microWatt
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RO
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Also see the Alarms section for status flags associated with power readings.
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******
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Energy
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******
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`energy[1-*]_input`
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Cumulative energy use
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Unit: microJoule
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RO
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`energy[1-*]_enable`
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Enable or disable the sensors.
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When disabled the sensor read will return
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-ENODATA.
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- 1: Enable
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- 0: Disable
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RW
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********
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Humidity
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********
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`humidity[1-*]_input`
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Humidity.
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`humidity[1-*]_enable`
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Enable or disable the sensors.
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`humidity[1-*]_rated_min`
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Minimum rated humidity.
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`humidity[1-*]_rated_max`
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Maximum rated humidity.
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******
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Alarms
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******
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Each channel or limit may have an associated alarm file, containing a
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boolean value. 1 means than an alarm condition exists, 0 means no alarm.
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Usually a given chip will either use channel-related alarms, or
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limit-related alarms, not both. The driver should just reflect the hardware
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implementation.
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+-------------------------------+-----------------------+
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| **`in[0-*]_alarm`, | Channel alarm |
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| `curr[1-*]_alarm`, | |
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| `power[1-*]_alarm`, | - 0: no alarm |
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| `fan[1-*]_alarm`, | - 1: alarm |
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| `temp[1-*]_alarm`** | |
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| | RO |
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+-------------------------------+-----------------------+
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**OR**
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+-------------------------------+-----------------------+
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| **`in[0-*]_min_alarm`, | Limit alarm |
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| `in[0-*]_max_alarm`, | |
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| `in[0-*]_lcrit_alarm`, | - 0: no alarm |
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| `in[0-*]_crit_alarm`, | - 1: alarm |
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| `curr[1-*]_min_alarm`, | |
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| `curr[1-*]_max_alarm`, | RO |
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| `curr[1-*]_lcrit_alarm`, | |
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| `curr[1-*]_crit_alarm`, | |
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| `power[1-*]_cap_alarm`, | |
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| `power[1-*]_max_alarm`, | |
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| `power[1-*]_crit_alarm`, | |
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| `fan[1-*]_min_alarm`, | |
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| `fan[1-*]_max_alarm`, | |
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| `temp[1-*]_min_alarm`, | |
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| `temp[1-*]_max_alarm`, | |
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| `temp[1-*]_lcrit_alarm`, | |
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| `temp[1-*]_crit_alarm`, | |
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| `temp[1-*]_emergency_alarm`** | |
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+-------------------------------+-----------------------+
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Each input channel may have an associated fault file. This can be used
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to notify open diodes, unconnected fans etc. where the hardware
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supports it. When this boolean has value 1, the measurement for that
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channel should not be trusted.
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`fan[1-*]_fault` / `temp[1-*]_fault`
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Input fault condition.
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Some chips also offer the possibility to get beeped when an alarm occurs:
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`beep_enable`
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Master beep enable.
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`in[0-*]_beep`, `curr[1-*]_beep`, `fan[1-*]_beep`, `temp[1-*]_beep`,
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Channel beep.
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In theory, a chip could provide per-limit beep masking, but no such chip
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was seen so far.
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Old drivers provided a different, non-standard interface to alarms and
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beeps. These interface files are deprecated, but will be kept around
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for compatibility reasons:
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`alarms`
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Alarm bitmask.
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`beep_mask`
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Bitmask for beep.
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*******************
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Intrusion detection
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*******************
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`intrusion[0-*]_alarm`
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Chassis intrusion detection.
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`intrusion[0-*]_beep`
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Chassis intrusion beep.
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****************************
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Average sample configuration
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****************************
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Devices allowing for reading {in,power,curr,temp}_average values may export
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attributes for controlling number of samples used to compute average.
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+--------------+---------------------------------------------------------------+
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| samples | Sets number of average samples for all types of measurements. |
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| | |
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| | RW |
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+--------------+---------------------------------------------------------------+
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|
| in_samples | Sets number of average samples for specific type of |
|
|
| power_samples| measurements. |
|
|
| curr_samples | |
|
|
| temp_samples | Note that on some devices it won't be possible to set all of |
|
|
| | them to different values so changing one might also change |
|
|
| | some others. |
|
|
| | |
|
|
| | 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 */
|