[CS-FSLUG] Linux Kernel, Thermal Monitoring, Broken ACPI

[Ed Hurst]

Machine: HP Pavilion 542x, sporting an Intel Celeron 1.8Ghz (P4)

Background: HP configures their BIOS to report temps in Centigrade instead  
of the standard Kelvin. Thus, Linux and BSD reports temps such as -269C.  
All distros I've been able to install do the same thing, as does FreeBSD.  
While there are supposed to be ways to write a new DSTD.aml and pass it to  
the kernel, with modifications to make it read right, I've not gotten that  
to work.

For now, I have CentOS 5.3 (my preference) running with 'acpi=off'. I  
don't mind if that's the best I can do, but it keeps the fan running. This  
happens to be a big gamer fan, the only replacement part available locally  
at the time, so it's pretty noisy.

Symptoms: The fan typically does not run under ACPI, but when it needs to  
come on, the kernel notices it cannot be turned off. When I check in  
/proc/acpi/thermal_zone/THRM/ I find polling is disabled, and the tipping  
points are all absurd negative values. I can correct those values, but I  
cannot correct the reporting temp. Periodically, the kacpi function tries  
to the switch, can't do anything, and spews loads of notices in the logs,  
while bogging down the system briefly. The notices are simply complaining  
the fan cannot be turned off.

To my knowledge, HP has no interest in fixing this, particulary such an  
old machine. Is there a way to tell the kernel to ignore thermal  
monitoring? A reliable way to present a translator to either read the  
values directly in C or translate them to K? There are some kernel patches  
floating around, but only for the the most recent series, and nothing for  
the stock RedHat/CentOS kernel (2.6.18).

I've been reading about this for about a week. There is a wide gap between  
HOWTOs and the esoteric discussion among the code gods. Anybody have a  
better idea than just leaving the fan running full bore?

-- 
Ed Hurst
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