IBM Thinkpad Fan Control (acpi_ibm)

Fredrik Lindberg fli+freebsd-current at
Wed Dec 21 05:26:26 PST 2005

Tobias Roth wrote:
> Hi
> With acpi_ibm.ko, I can monitor fan speed, thermal sensors and do
> many other nice things. However, my Thinkpad (a T43p) has an awfully
> noisy fan, that, once the notebook reaches its standard working
> temperature (around 45 deg C), turns on and never stops again. 
> The generally accepted solution his to manually lower the fan speed
> and live with the higher temperatures, which will still be in an
> acceptable range even with slow running fans. The discussion and a
> utility for Windows can be found here [1], and a linux tool is
> described here [2]. 
> Now my question. Since acpi_ibm.ko can already read temperature
> sensors and fan speed, would it be feasable to teach it to control
> fan speed as well? Is anyone working on it already? Or can someone
> outline the steps that have to be taken so I can take a look and  
> see if I can do it myself?
> thanks, t.

I don't know if somebody is working on it, but it shouldn't be too
hard to add it to acpi_ibm.
Just parse the relevant bits from the linux patch and add a new
sysctl method for fan speed in the acpi_ibm_sysctl_set() function in
the file sys/dev/acpi_support/acpi_ibm.c

I did this a while ago for but for fan enable/disable, but that is
really useless because the only thing you can accomplish with the
fan off is a fried laptop (although, it will be quiet :)).

It's probably quite dangerous to mess with the fan speed too, because
even if the fan is running at low speed you risk overheating your

Fredrik Lindberg

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