SPCR

Is there any doable (by which I mean aside of hacking cpufreq's K8 settings) to get other P states running under Linux?

My Athlon64 works rock solid at 1800/1.25V but when I set voltages by hand, the A8V doesn't do any cool & quiet anymore (and neither will do cpufreq from what I gather).

So basically, I'm out to get cool&quiet to run with 1.25V at full speed and something like 1.0V or so at 1GHz. Is that even possible under Linux? Or do I need to go patch the kernel first?

Have you tried cpudyn?
I think that could be what you need.

There's a thread on the Gentoo Linux forums about it.