501 lines
15 KiB
Plaintext
501 lines
15 KiB
Plaintext
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. See libsensors documentation and source for
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further information. As of writing this document, libsensors
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(from lm_sensors 2.8.3) is heavily chip-dependent. Adding or updating
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support for any given chip requires modifying the library's code.
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This is because libsensors was written for the procfs interface
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older kernel modules were using, which wasn't standardized enough.
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Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
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support for the sysfs interface, though.
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The new sysfs interface was designed to be as chip-independent as
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possible.
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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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If you are developing a userspace application please send us feedback on
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this standard.
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Note that this standard isn't completely established yet, so it is subject
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to changes. If you are writing a new hardware monitoring driver those
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features can't seem to fit in this interface, please contact us with your
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extension proposal. Keep in mind that backward compatibility must be
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preserved.
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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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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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-------------------------------------------------------------------------
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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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RW read/write value
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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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********
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* Name *
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********
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name The chip name.
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This should be a short, lowercase string, not containing
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spaces nor dashes, representing the chip name. This is
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the only mandatory attribute.
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I2C devices get this attribute created automatically.
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RO
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************
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* Voltages *
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************
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in[0-*]_min Voltage min value.
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Unit: millivolt
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RW
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in[0-*]_max Voltage max value.
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Unit: millivolt
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RW
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in[0-*]_input Voltage input value.
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Unit: millivolt
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RO
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Voltage measured on the chip pin.
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Actual voltage depends on the scaling resistors on the
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motherboard, as recommended in the chip datasheet.
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This varies by chip and by motherboard.
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Because of this variation, values are generally NOT scaled
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by the chip driver, and must be done by the application.
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However, some drivers (notably lm87 and via686a)
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do scale, because of internal resistors built into a chip.
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These drivers will output the actual voltage. Rule of
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thumb: drivers should report the voltage values at the
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"pins" of the chip.
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in[0-*]_label Suggested voltage channel label.
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Text string
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Should only be created if the driver has hints about what
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this voltage channel is being used for, and user-space
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doesn't. In all other cases, the label is provided by
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user-space.
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RO
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cpu[0-*]_vid CPU core reference voltage.
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Unit: millivolt
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RO
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Not always correct.
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vrm Voltage Regulator Module version number.
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RW (but changing it should no more be necessary)
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Originally the VRM standard version multiplied by 10, but now
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an arbitrary number, as not all standards have a version
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number.
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Affects the way the driver calculates the CPU core reference
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voltage from the vid pins.
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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 Fan minimum value
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Unit: revolution/min (RPM)
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RW
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fan[1-*]_input Fan input value.
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Unit: revolution/min (RPM)
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RO
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fan[1-*]_div Fan divisor.
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Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
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RW
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Some chips only support values 1, 2, 4 and 8.
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Note that this is actually an internal clock divisor, which
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affects the measurable speed range, not the read value.
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fan[1-*]_target
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Desired fan speed
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Unit: revolution/min (RPM)
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RW
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Only makes sense if the chip supports closed-loop fan speed
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control based on the measured fan speed.
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fan[1-*]_label Suggested fan channel label.
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Text string
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Should only be created if the driver has hints about what
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this fan channel is being used for, and user-space doesn't.
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In all other cases, the label is provided by user-space.
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RO
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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-*] Pulse width modulation fan control.
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Integer value in the range 0 to 255
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RW
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255 is max or 100%.
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pwm[1-*]_enable
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Fan speed control method:
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0: no fan speed control (i.e. fan at full speed)
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1: manual fan speed control enabled (using pwm[1-*])
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2+: automatic fan speed control enabled
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Check individual chip documentation files for automatic mode
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details.
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RW
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pwm[1-*]_mode 0: DC mode (direct current)
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1: PWM mode (pulse-width modulation)
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RW
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pwm[1-*]_freq Base PWM frequency in Hz.
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Only possibly available when pwmN_mode is PWM, but not always
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present even then.
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RW
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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. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
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Which values are possible depend on the chip used.
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RW
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pwm[1-*]_auto_point[1-*]_pwm
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pwm[1-*]_auto_point[1-*]_temp
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pwm[1-*]_auto_point[1-*]_temp_hyst
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Define the PWM vs temperature curve. Number of trip points is
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chip-dependent. Use this for chips which associate trip points
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to PWM output channels.
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RW
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OR
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temp[1-*]_auto_point[1-*]_pwm
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temp[1-*]_auto_point[1-*]_temp
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temp[1-*]_auto_point[1-*]_temp_hyst
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Define the PWM vs temperature curve. Number of trip points is
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chip-dependent. Use this for chips which associate trip points
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to temperature channels.
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RW
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****************
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* Temperatures *
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****************
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temp[1-*]_type Sensor type selection.
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Integers 1 to 6
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RW
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1: PII/Celeron Diode
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2: 3904 transistor
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3: thermal diode
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4: thermistor
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5: AMD AMDSI
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6: Intel PECI
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Not all types are supported by all chips
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temp[1-*]_max Temperature max value.
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Unit: millidegree Celsius (or millivolt, see below)
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RW
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temp[1-*]_min Temperature min value.
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Unit: millidegree Celsius
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RW
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temp[1-*]_max_hyst
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Temperature hysteresis value for max limit.
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Unit: millidegree Celsius
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Must be reported as an absolute temperature, NOT a delta
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from the max value.
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RW
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temp[1-*]_input Temperature input value.
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Unit: millidegree Celsius
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RO
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temp[1-*]_crit Temperature critical value, typically greater than
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corresponding temp_max values.
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Unit: millidegree Celsius
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RW
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temp[1-*]_crit_hyst
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Temperature hysteresis value for critical limit.
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Unit: millidegree Celsius
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Must be reported as an absolute temperature, NOT a delta
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from the critical value.
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RW
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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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Unit: millidegree Celsius
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Read/Write value.
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temp[1-*]_label Suggested temperature channel label.
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Text string
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Should only be created if the driver has hints about what
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this temperature channel is being used for, and user-space
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doesn't. In all other cases, the label is provided by
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user-space.
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RO
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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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Note that no known chip provides current measurements as of writing,
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so this part is theoretical, so to say.
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curr[1-*]_max Current max value
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Unit: milliampere
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RW
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curr[1-*]_min Current min value.
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Unit: milliampere
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RW
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curr[1-*]_input Current input value
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Unit: milliampere
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RO
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*********
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* Power *
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*********
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power[1-*]_average Average power use
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Unit: microWatt
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RO
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power[1-*]_average_highest Historical average maximum power use
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Unit: microWatt
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RO
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power[1-*]_average_lowest Historical average minimum power use
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Unit: microWatt
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RO
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power[1-*]_input Instantaneous power use
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Unit: microWatt
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RO
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power[1-*]_input_highest Historical maximum power use
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Unit: microWatt
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RO
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power[1-*]_input_lowest Historical minimum power use
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Unit: microWatt
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RO
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power[1-*]_reset_history Reset input_highest, input_lowest,
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average_highest and average_lowest.
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WO
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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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in[0-*]_alarm
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fan[1-*]_alarm
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temp[1-*]_alarm
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Channel alarm
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0: no alarm
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1: alarm
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RO
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OR
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in[0-*]_min_alarm
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in[0-*]_max_alarm
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fan[1-*]_min_alarm
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temp[1-*]_min_alarm
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temp[1-*]_max_alarm
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temp[1-*]_crit_alarm
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Limit alarm
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0: no alarm
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1: alarm
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RO
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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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in[0-*]_fault
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fan[1-*]_fault
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temp[1-*]_fault
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Input fault condition
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0: no fault occured
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1: fault condition
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RO
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Some chips also offer the possibility to get beeped when an alarm occurs:
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beep_enable Master beep enable
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0: no beeps
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1: beeps
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RW
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in[0-*]_beep
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fan[1-*]_beep
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temp[1-*]_beep
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Channel beep
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0: disable
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1: enable
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RW
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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 Alarm bitmask.
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RO
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Integer representation of one to four bytes.
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A '1' bit means an alarm.
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Chips should be programmed for 'comparator' mode so that
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the alarm will 'come back' after you read the register
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if it is still valid.
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Generally a direct representation of a chip's internal
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alarm registers; there is no standard for the position
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of individual bits. For this reason, the use of this
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interface file for new drivers is discouraged. Use
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individual *_alarm and *_fault files instead.
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Bits are defined in kernel/include/sensors.h.
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beep_mask Bitmask for beep.
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Same format as 'alarms' with the same bit locations,
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use discouraged for the same reason. Use individual
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*_beep files instead.
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RW
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sysfs attribute writes interpretation
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-------------------------------------
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hwmon sysfs attributes always contain numbers, so the first thing to do is to
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convert the input to a number, there are 2 ways todo this depending whether
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the number can be negative or not:
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unsigned long u = simple_strtoul(buf, NULL, 10);
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long s = simple_strtol(buf, NULL, 10);
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With buf being the buffer with the user input being passed by the kernel.
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Notice that we do not use the second argument of strto[u]l, and thus cannot
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tell when 0 is returned, if this was really 0 or is caused by invalid input.
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This is done deliberately as checking this everywhere would add a lot of
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code to the kernel.
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Notice that it is important to always store the converted value in an
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unsigned long or long, so that no wrap around can happen before any further
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checking.
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After the input string is converted to an (unsigned) long, the value should be
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checked if its acceptable. Be careful with further conversions on the value
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before checking it for validity, as these conversions could still cause a wrap
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around before the check. For example do not multiply the result, and only
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add/subtract if it has been divided before the add/subtract.
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What to do if a value is found to be invalid, depends on the type of the
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sysfs attribute that is being set. If it is a continuous setting like a
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tempX_max or inX_max attribute, then the value should be clamped to its
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limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
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continuous like for example a tempX_type, then when an invalid value is
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written, -EINVAL should be returned.
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Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
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long v = simple_strtol(buf, NULL, 10) / 1000;
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v = SENSORS_LIMIT(v, -128, 127);
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/* write v to register */
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Example2, fan divider setting, valid values 2, 4 and 8:
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unsigned long v = simple_strtoul(buf, NULL, 10);
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switch (v) {
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case 2: v = 1; break;
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case 4: v = 2; break;
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case 8: v = 3; break;
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default:
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return -EINVAL;
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}
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/* write v to register */
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