why use acpi for cpufreq?

I've recently been bitten by http://bugzilla.kernel.org/show_bug.cgi?id=7157 - I also have an HP nc6400, with bios F.05, and can't downgrade to F.03 because my CPU only became supported in F.05. While I'm waiting to see if HP will fix this problem in a future bios rev, I wondered why cpufreq needs any bios information in the first place?

This is all well outside my technical expertise, so I'm sure that I'm misunderstanding the problem - but that's why I'm asking. Basically my question is: why can't cpufreq interrogate the CPU directly, in order to find out what sort of cpu frequency scaling it supports (SpeedStep in various flavors, PowerNow, and whatever else is out there in the wild)? Wouldn't that be more robust than relying on the bios to get it right?

As a side issue, how does Windows XP solve this problem? From what I can tell, Windows XP does use frequency-scaling with my CPU (according to the NHC software from http://www.pbus-167.com/).

Again, I'm sure that I'm misunderstanding the technical issues here, but I'd like to understand them. I'm also happy to post a summary on the acpi wiki, so that the question is less likely to come up again.

thanks,
-- Mike

Hi,

Unfortunately, no -- it is not only a matter of the processor on whether CPU frequency and voltage scaling is supported, but also a matter of the motherboard. Not all combinations of frequencies and voltages which run stable on one notebook may run well on a different notebook with the same CPU. Therefore, such hardcoded table-based approaches are only available in rare cases.

Dominik