[ltp] Noisy fan on T42

[Alexandru D. Salcianu]

Hello!

Many thanks to all the people who replied to my email!  Unfortunately,
my fan is still on and noisy (honestly, did anyone ever managed to
stop a T42 fan?  I started to doubt this ...)

Here is a brief update of the progress so far:

1. First, as a quick reminder, my problem is that the fan is always on
   and noisy in Linux, even if I don't run anything intensive and I
   set the proc. speed to the minimum 600MHz.  Config: IBM ThinkPad
   T42 2373-6VU, 1.7GHz Centrino, ATI Radeon 7500, running Fedora Core
   3, kernel 2.6.10-1.770_FC3, Xorg 6.8.1

2. To answer some of the previous emails, I have verified in
   /proc/cpuinfo and the processor speed is indeed 600MHz (as I want
   it to be).  My kernel runs ACPI (not APM).  I have also downloaded
   and installed the latest ibm_acpi kernel module (0.10) from
   ibm-acpi.sf.net.

3. I have verified in the Xorg.0.log, and the dynamic clock scaling
   (for the video card) is enabled in the radeon video driver:

   (II) RADEON(0): Dynamic Clock Scaling Enabled

I've noticed the following scenario: when I first start the machine,
the fan is running at some normal speed (although it is clearly on).
When I run some moderate/intensive computation, the CPU temperature
increases, and the fan starts running 100% speed, generating an
unpleasant noise.  Next, even after the intensive computation
terminates and the CPU temperature goes down to 42 C, the fan still
stays at 100% ...  The fan never comes back to a normal speed.

[ I'm using "cat /proc/acpi/thermal_zone/THM0/tempreature" to measure
the CPU temperature; the readings are compatible with those reported
by "cat /proc/acpi/ibm/thermal". ]

Is this normal?  Shouldn't the fan lower its speed at 42C (it seems a
pretty low temperature) or even better, stop?  The ibm-acpi doc from
http://ibm-acpi.sourceforge.net/README states that on an X40, "the fan
is turned off when the CPU temperature drops to 49 degrees".  Why is
T42 not behaving in a similar fashion?

I have no idea what the other temperatures indicated by the ibm-acpi
mean, but here they are:

[ibm]# cat thermal 
temperatures:   43 47 34 49 33 -128 28 -128
fan_speed:      3582
fan_offset:     0x84
commands:       fan_offset <offset> (<offset> is 0x00-0xff)

[ I'm highly reluctant to play directly with the fan speed; I don't
want my laptop to melt. ]

Thank you in advance for any suggestions you may have!

Alex