High fan speed after return from suspend (on Ubuntu)

Question

I've got a HP ProBook 5310m laptop with Ubuntu 10.04 (32 bit). When I return from suspend, the fan speed is usually very high: FDTZ sensor reports "90 °C". Yes, the units are wrong, since FDTZ does not report temperature, but fan speed – that's probably just a small bug in reporting. Interestingly, when I plug or unplug the power cable for a moment, the fan speed returns back to normal.

My questions:

1. Where can I report this problem? Is it about ACPI support in the kernel? What is the address of the relevant bug tracker?
2. As a workaround for now, how can I programmatically trigger a behavior equivalent to (un)plugging the power cable. More generally, how can I force ACPI to recalculate fan speed? Ideally, I'm looking for something like echo foo > /proc/bar.

Thanks in advance!

Answer 1

In my case, a workaround for now is to issue this command after suspend (as root):

echo 0 > /proc/acpi/fan/FAN5/state

This command switches on a device – sets its power state to D0. Apparently, it can also be used to "reset" a fan that is already on. After that operation, the fan runs at normal speed (30 °C). How did I know which fan to touch? I looked for a fan with "on" status:

grep on /proc/acpi/fan/*/state

It seems that a fairly similar issue has already been added to the Kernel Bug Tracker.