linux-kernel - Re: [PATCH 1/1] cpufreq: eeepc 900 frequency scaling driver

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Message-ID: <492ADA81.4070904@compton.nu>
Date:	Mon, 24 Nov 2008 16:46:57 +0000
From:	Tom Hughes <tom@...pton.nu>
To:	Thomas Renninger <trenn@...e.de>
CC:	Cristiano Prisciandaro <cristiano.p@...net.ch>,
	Dave Jones <davej@...hat.com>, cpufreq@...r.kernel.org,
	linux-kernel@...r.kernel.org, acpi4asus-user@...ts.sourceforge.net
Subject: Re: [PATCH 1/1] cpufreq: eeepc 900 frequency scaling driver

Thomas Renninger wrote:

> Oh, they are part of this general Asus \\_SB.ATKD device, which is only
> used by asus_laptop.c until now?

I believe eeepc-laptop is also accessing the same device - at least it 
is calling other methods defined in the same part of the DSDT although 
it doesn't seem to be using that name to reach them.

> Some more questions:
> Why are they providing their own cpufreq interface and not following the
> spec (providing _PSS, ..)?
> Could it be that you are only throttling the CPU?
>
> Are these functions already used by the ACPI tables internally?
>   - could be dangerous
>   - could be helpful -> Is there some upper level device/interface in ASL?
> 
> Could it happen that upcoming machines provide this interface (the two ACPI 
> functions) and also can do real CPU frequency/volt switching, e.g. via 
> acpi-cpufreq?

Well the recent eee's are all Atom based, which I assume has proper 
SpeedStep support but the early ones have a Celeron processor.

The history is that the original eee, the 701, was underclocking a 
900MHz CPU at 630Mhz and in the 900 they added support for running at 
full speed with the BIOS able to switch between the two speeds. I assume 
it just changes the clock multiplier or something.

The 901 and later of course use the Atom and presumably work differently.

Tom

-- 
Tom Hughes (tom@...pton.nu)
http://www.compton.nu/
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