forked from Minki/linux
0750b8fcf3
Add documentation for the newly added attributes: fine_grain_control fan_speed_rpm Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
91 lines
3.3 KiB
ReStructuredText
91 lines
3.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===========================
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ACPI Fan Performance States
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===========================
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When the optional _FPS object is present under an ACPI device representing a
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fan (for example, PNP0C0B or INT3404), the ACPI fan driver creates additional
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"state*" attributes in the sysfs directory of the ACPI device in question.
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These attributes list properties of fan performance states.
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For more information on _FPS refer to the ACPI specification at:
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http://uefi.org/specifications
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For instance, the contents of the INT3404 ACPI device sysfs directory
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may look as follows::
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$ ls -l /sys/bus/acpi/devices/INT3404:00/
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total 0
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...
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state0
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state1
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state10
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state11
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state2
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state3
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state4
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state5
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state6
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state7
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state8
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-r--r--r-- 1 root root 4096 Dec 13 20:38 state9
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-r--r--r-- 1 root root 4096 Dec 13 01:00 status
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...
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where each of the "state*" files represents one performance state of the fan
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and contains a colon-separated list of 5 integer numbers (fields) with the
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following interpretation::
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control_percent:trip_point_index:speed_rpm:noise_level_mdb:power_mw
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* ``control_percent``: The percent value to be used to set the fan speed to a
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specific level using the _FSL object (0-100).
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* ``trip_point_index``: The active cooling trip point number that corresponds
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to this performance state (0-9).
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* ``speed_rpm``: Speed of the fan in rotations per minute.
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* ``noise_level_mdb``: Audible noise emitted by the fan in this state in
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millidecibels.
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* ``power_mw``: Power draw of the fan in this state in milliwatts.
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For example::
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$cat /sys/bus/acpi/devices/INT3404:00/state1
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25:0:3200:12500:1250
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When a given field is not populated or its value provided by the platform
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firmware is invalid, the "not-defined" string is shown instead of the value.
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ACPI Fan Fine Grain Control
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=============================
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When _FIF object specifies support for fine grain control, then fan speed
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can be set from 0 to 100% with the recommended minimum "step size" via
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_FSL object. User can adjust fan speed using thermal sysfs cooling device.
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Here use can look at fan performance states for a reference speed (speed_rpm)
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and set it by changing cooling device cur_state. If the fine grain control
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is supported then user can also adjust to some other speeds which are
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not defined in the performance states.
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The support of fine grain control is presented via sysfs attribute
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"fine_grain_control". If fine grain control is present, this attribute
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will show "1" otherwise "0".
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This sysfs attribute is presented in the same directory as performance states.
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ACPI Fan Performance Feedback
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=============================
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The optional _FST object provides status information for the fan device.
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This includes field to provide current fan speed in revolutions per minute
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at which the fan is rotating.
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This speed is presented in the sysfs using the attribute "fan_speed_rpm",
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in the same directory as performance states.
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