ACPI Fan Performance States

When the optional _FPS object is present under an ACPI device representing a fan (for example, PNP0C0B or INT3404), the ACPI fan driver creates additional “state*” attributes in the sysfs directory of the ACPI device in question. These attributes list properties of fan performance states.

For more information on _FPS refer to the ACPI specification at:

http://uefi.org/specifications

For instance, the contents of the INT3404 ACPI device sysfs directory may look as follows:

$ ls -l /sys/bus/acpi/devices/INT3404:00/
total 0
...
-r--r--r-- 1 root root 4096 Dec 13 20:38 state0
-r--r--r-- 1 root root 4096 Dec 13 20:38 state1
-r--r--r-- 1 root root 4096 Dec 13 20:38 state10
-r--r--r-- 1 root root 4096 Dec 13 20:38 state11
-r--r--r-- 1 root root 4096 Dec 13 20:38 state2
-r--r--r-- 1 root root 4096 Dec 13 20:38 state3
-r--r--r-- 1 root root 4096 Dec 13 20:38 state4
-r--r--r-- 1 root root 4096 Dec 13 20:38 state5
-r--r--r-- 1 root root 4096 Dec 13 20:38 state6
-r--r--r-- 1 root root 4096 Dec 13 20:38 state7
-r--r--r-- 1 root root 4096 Dec 13 20:38 state8
-r--r--r-- 1 root root 4096 Dec 13 20:38 state9
-r--r--r-- 1 root root 4096 Dec 13 01:00 status
...

where each of the “state*” files represents one performance state of the fan and contains a colon-separated list of 5 integer numbers (fields) with the following interpretation:

control_percent:trip_point_index:speed_rpm:noise_level_mdb:power_mw

  • control_percent: The percent value to be used to set the fan speed to a specific level using the _FSL object (0-100).

  • trip_point_index: The active cooling trip point number that corresponds to this performance state (0-9).

  • speed_rpm: Speed of the fan in rotations per minute.

  • noise_level_mdb: Audible noise emitted by the fan in this state in millidecibels.

  • power_mw: Power draw of the fan in this state in milliwatts.

For example:

$cat /sys/bus/acpi/devices/INT3404:00/state1
25:0:3200:12500:1250

When a given field is not populated or its value provided by the platform firmware is invalid, the “not-defined” string is shown instead of the value.