linux-kernel - Re: Possible bug in eeepc-laptop.c

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Date:	Wed, 17 Mar 2010 14:49:13 +0000
From:	Alan Jenkins <sourcejedi.lkml@...glemail.com>
To:	Fabio Comolli <fabio.comolli@...il.com>
Cc:	Corentin Chary <corentin.chary@...il.com>,
	ACPI mailing list <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>
Subject: Re: Possible bug in eeepc-laptop.c - EeePC 900

On 3/13/10, Fabio Comolli <fabio.comolli@...il.com> wrote:
> Well, I'm confused.
>
> I rebooted with the "vanilla" eeepc-laptop.c and I'm sorry to say that
> the situation it's not like the one I described in the post I wrote 2
> days ago. Actually the situation with the patch reverted is the same I
> have with the patch applied.
>
> What I mean is that if I boot on AC power /proc/cpuinfo always reports
> 900MHz and 1800 bogomips. It I boot on battery /proc/cpuinfo always
> reports 630MHz and 1260 bogomips. Plugging / unplugging the AC does
> not change the situation. Only reboot does.
>
> But the cpufv interface does indeed seem to work, as glxgears and
> stellarium show the frame rate change accordingly to the powersave /
> performance selection.
>
> So my question is: what does really the cpufv interface do? Is it
> supposed to change the processor frequency?

Yes, writing to cpufv asks the BIOS to set the CPU speed.

> And if the answer to the latest question is affirmative, why
> /proc/cpuinfo seems to ignore it?

It's because eeepc-laptop doesn't register as a real cpufreq driver.
The BIOS doesn't tell us what frequency it switches to.  Theoretically
you could re-use the boot code, but I'm not sure how you would make it
co-operate with the cpufreq core.

Alan
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