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

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

On Tue, 6 Jan 2004, Defiant wrote:
> >> CONFIG_X86_ACPI_CPUFREQ=y
> >> CONFIG_X86_ACPI_CPUFREQ_PROC_INTF=y
> >
> > Please try patch filed at
> > http://bugzilla.kernel.org/show_bug.cgi?id=1489
>
> Tried the patch, but it didn't solved the Problem.
>
> Well at least I found out some more Info about.
> My full speed is 1600, low speed is 1200Mhz:
>
> When running on AC Adapter, I can switch the speed as often as I want.
> So If I set it to 1200 and then disconnect the AC, I can also switch
> between both speeds under battery power. Now If it is 1200 and I connect
> the AC I can not set it back to 1600.
> Well like I said in my preceding post it is the same: Running with AC,
> speed set to 1600, disconnecting the AC, I can not set the speed down to
> 1200.

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.

-Nate


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