Patch for controlling fan speed

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Revision as of 13:36, 22 August 2006 by Dimeco (Talk | contribs) (for ibm-acpi 0.12a as found in kernel 2.6.14)
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This patch extends the ibm-acpi Linux kernel module to control fan speed. It can be used to reduce fan noise (both speed and pulsing) and to decrease fan power consumption.

When this patch is applied and the ibm-acpi module is loaded with the experimental=1 module parameter, the following new capabilities are added to /proc/acpi/ibm/fan:

  • # echo level LEVEL > /proc/acpi/ibm/fan sets a fan speed level between 0 and 7, where LEVEL=0 means fan off and LEVEL=7 is the fastest speed.
  • # echo level auto > /proc/acpi/ibm/fan tells the embedded controller to set the fan speed automatically according to system temperatures (this is the default).
  • # echo level disengaged > /proc/acpi/ibm/fan tells the embedded controller to disengage fan speed control (see specs below).
  • # cat /proc/acpi/ibm/fan shows the current fan level (in addition to the fan speed in RPM).

For example:

#cat /proc/acpi/ibm/fan
status:         enabled
level:          auto
speed:          4219
commands:       enable, disable, level <level>
                (<level> is 0-7, auto or disengaged)

#echo level 2 > /proc/acpi/ibm/fan

#cat /proc/acpi/ibm/fan
status:         enabled
level:          2
speed:          3142
commands:       enable, disable, level <level>
                (<level> is 0-7, auto or disengaged)

This patch is best used with an ACPI fan control script that monitors system temperature and sets the fan speed accordingly.

Overriding the system's automatic temperature control may cause permanent hardware damage. Even when using temperature monitoring software, it is not clear whether the software can access all temperature sensor accessible to the embedded controller and understand them correctly. Moreover, this patch relies on an undocumented hardware interface, and may thus have arbitrary effects (especially on models it wasn't tested on).

The patch

for ibm-acpi 0.11

ibm-acpi-0.11-2.6.13-fan.patch (download)

This also includes a minor fix (rename of device_add) to make ibm-acpi 0.11 compile on kernel 2.6.13.

for ibm-acpi 0.12a as found in kernel 2.6.14 and 2.6.17

A slightly modified version which also keeps the lines in the format expected by the gkrellm plugin.

ibm-acpi-0.12a-2.6.14-fan.patch (download)

ibm-acpi-0.12a-2.6.17-fan.patch (download)

In order to patch the ibm_acpi.c file you have tu issue the following command: patch -p0 -l < fanpatch. The '-l' option is important because if the patch pasted here doesn't have any tabs any more. Another advice: Always try to patch the files first before really patching it. That is done by adding --dry-run to the command.

Ideas for improvement

  • When fan speed is controlled from userspace (e.g., by the ACPI fan control scripts), the userspace component may die (for whatever reason) leaving the fan at a low speed, potentially leading to damage. We can add a watchdog to the kernel component, which resets the fan to Embedded Controller control (leve: auto) if /proc/acpi/ibm/fan was not written to for N seconds.

Alternative methods and hardware specs

See How to control fan speed.

Supported models

See How to control fan speed.