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

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Message-ID: <b637ec0b1003170840j5a8ed0c8nda3b7890caf0a855@mail.gmail.com>
Date:	Wed, 17 Mar 2010 16:40:24 +0100
From:	Fabio Comolli <fabio.comolli@...il.com>
To:	Alan Jenkins <sourcejedi.lkml@...glemail.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

Hi

On Wed, Mar 17, 2010 at 3:49 PM, Alan Jenkins
<sourcejedi.lkml@...glemail.com> wrote:
> 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.

OK

>
>> 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.

OK, now I understand. Thanks. So it seems that the only way to get the
actual CPU frequency is to query the cpufv sysfs file. Good to know.

Unless someone with the required knowledge comes up with the code
needed to register eeepc-laptop as a real cpufreq driver (hint, hint
:-) )

>
> Alan
>

Thanks,
Fabio
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