linux-kernel - Re: Ubuntu patch enabling speedstep for sonoma processors

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Date:	Thu, 24 Jun 2010 18:29:32 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Ozan Çağlayan <ozan@...dus.org.tr>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ubuntu Kernel Team <kernel-team@...ts.ubuntu.com>,
	Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: Ubuntu patch enabling speedstep for sonoma processors

On 06/24/2010 09:50 AM, Ozan Çağlayan wrote:
> Hi,
>
> The following patch enables speedstep for sonoma processors:
> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-maverick.git;a=blobdiff;f=arch/x86/kernel/cpu/cpufreq/speedstep-centrino.c;h=ee4e9f8050752923f9671f61ffbea662bc9ad12a;hp=9b1ff37de46ae6a729f48d2d94ad30548806884d;hb=23120eb5ae5a12924565e8af3d946a015e1caaf9;hpb=215cc71ef0b26b9434404f387681d9bd173d2434
>
> The patch never got accepted by upstream after some discussions:
>
> http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-06/msg01078.html
>
> """
> This patch has been floating around for years.
> So long, I've forgotten the original reason it wasn't accepted.
> It had something to do with it working for some users, but not others,
> and we can't detect the 'not working' case.
>
> speedstep-centrino is also deprecated in favour of acpi-cpufreq for some time.
> If acpi isn't working on these machines, we should find out why.
>
> Dave Jones
> """
>
> """
> My recollection is that we had no way to work out which voltage table
> was appropriate for a given CPU, so there was a risk of us either over-
> or under-volting the chip. Doing it via ACPI is safe.
>
> Matthew Garrett
> """
>
> I have bug report from a user which complains that frequency scaling is not available
> on its computer. This patch fixes the issue but seen the discussions there should be a
> better and more correct way to fix the issue.
>
> What should I do in order to debug and try to fix it?
>
> And also seen that Ubuntu carries this patch for a relatively long time, did you see
> any negative effect like the aforementioned risk of over/under-volting the chip?

The acpidump from that system would be a good start, to figure out why 
acpi-cpufreq isn't working..
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