RE: can't switch CPU frequency while running on batterypower

[Nate Lawson <nate-Y6VGUYTwhu0@public.gmane.org>]

On Tue, 6 Jan 2004, Defiant wrote:
> Nate Lawson wrote:
> > This is most likely a problem with re-evaluation of _PSS after it has been
> > changed.  I don't remember if Linux uses the notify on the processor
> > object to re-evaluate _PSS.  If Linux does this correctly, it may be that
> > the underlying firmware has a bug and you should use a more specific
> > cpufreq driver (i.e. SpeedStep or whatever).  Some systems have a problem
> > where they don't properly export firmware information to the ACPI
> > performance states interface.
>
> uhm, I don't know why, but it is working now, using
> CONFIG_X86_P4_CLOCKMOD instead of CONFIG_X86_SPEEDSTEP_ICH, even it is a
> Pentium 4m, not Pentium 4.

Sure.  In general, it's better to use a hw-specific cpufreq driver instead
of the generic ACPI one, even if the latter seems to work.  Many chipsets
don't export the hw-specific information to ACPI correctly and thus ACPI
performance states cpufreq should be a last resort.  If they still don't
work, you should try multiple hw-specific drivers, as you did.

-Nate


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