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

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Message-ID: <9b2b86520902190354m259f85d0n97795da7b1b8afdd@mail.gmail.com>
Date:	Thu, 19 Feb 2009 11:54:06 +0000
From:	Alan Jenkins <sourcejedi.lkml@...glemail.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	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 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.

Alan
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