sysfs-interface

linux 内核源代码

Naming and data format standards for sysfs files
------------------------------------------------

The libsensors library offers an interface to the raw sensors data
through the sysfs interface. See libsensors documentation and source for
further information. As of writing this document, libsensors
(from lm_sensors 2.8.3) is heavily chip-dependent. Adding or updating
support for any given chip requires modifying the library's code.
This is because libsensors was written for the procfs interface
older kernel modules were using, which wasn't standardized enough.
Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
support for the sysfs interface, though.

The new sysfs interface was designed to be as chip-independent as
possible.

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.

If you are developing a userspace application please send us feedback on
this standard.

Note that this standard isn't completely established yet, so it is subject
to changes. If you are writing a new hardware monitoring driver those
features can't seem to fit in this interface, please contact us with your
extension proposal. Keep in mind that backward compatibility must be
preserved.

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*.

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
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.


********
* Name *
********

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


************
* Voltages *
************

in[0-*]_min	Voltage min value.
		Unit: millivolt
		RW
		
in[0-*]_max	Voltage max value.
		Unit: millivolt
		RW
		
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-*]_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-*]_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-*]_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

OR

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


****************
* Temperatures *
****************

temp[1-*]_type	Sensor type selection.
		Integers 1 to 6
		RW
		1: PII/Celeron Diode
		2: 3904 transistor
		3: thermal diode
		4: thermistor
		5: AMD AMDSI