linux-kernel - Re: [PATCH] cpufreq: Change link order of x86 cpufreq modules

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Date:	Mon, 23 Feb 2009 22:12:23 +0100
From:	Thomas Renninger <trenn@...e.de>
To:	alan-jenkins@...fmail.co.uk, Kay Sievers <kasievers@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>, Matthew Garrett <mjg59@...f.ucam.org>,
	davej@...emonkey.org.uk, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org
Subject: Re: [PATCH] cpufreq: Change link order of x86 cpufreq modules

On Thursday 19 February 2009 12:54:06 pm Alan Jenkins wrote:
> On 2/18/09, Ingo Molnar <mingo@...e.hu> wrote:
> > * Matthew Garrett <mjg59@...f.ucam.org> wrote:
> >> On Wed, Feb 18, 2009 at 07:31:37PM +0100, Ingo Molnar wrote:
> >> > Nice fix! Where does this information come from? Distro module
> >> > ordering magic? It's rather non-trivial.
> >>
> >> Pretty much. p4-clockmod is never the preferred option because
> >> it does no voltage scaling. speedstep-centrino is now almost
> >> entirely functionally replaced with acpi-cpufreq. The
> >> powernow-k8 issue was a personal communication from davej.
> >
> > I'm wondering whether that priority order should/could be
> > expressed in the module space too - so that distros wouldnt have
> > to replicate this. This is really a piece of information the
> > kernel is best at maintaining.
>
> The latest development version of module-init-tools (in the git tree)
> is designed to preserve the kernel link order when resolving builtin
> aliases.  If you have two modules which provide the alias "pci:123",
> they will be loaded in the same order as if they were builtin drivers.
>
> It should work if all the cpufreq drivers provide an alias
> "cpufreq-driver" and userspace just does "modprobe cpufreq-driver".
> You just need to be sure none of the cpufreq drivers provide *other*
> aliases which cause them to be loaded earlier, by udev or some other
> bootscript.
I wonder whether a "cpu:vendor:fam:model:flags:..." alias makes sense.
This would solve autoloading of most cpufreq drivers, but it never looked
important enough.
Other drivers that could make use of this:
  - k8temp/k10temp (Don't know about this one, but AFAIK there exists an
    MSR to read out temperature on latest AMD for which a hwmon driver
    is/should be written)?
  - Microcode update?
  - more?

     Thomas
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