Re: [PATCH 5/8] thermal:cpu cooling:tegra: Provide deferred probing for tegra driver

From: Lukasz Majewski
Date: Mon Nov 17 2014 - 07:52:12 EST

Hi Thierry,

> On Fri, Nov 14, 2014 at 12:24:37PM +0100, Lukasz Majewski wrote:
> > Hi Mikko,
> >
> > > Tested-by: Mikko Perttunen <mikko.perttunen@xxxxxxxx>
> >
> > Thanks for testing.
> >
> > >
> > > One potential issue I can see is that if the cpufreq driver fails
> > > to probe then you'll never get the thermal driver either. For
> > > example, Tegra124 currently has no cpufreq driver, so if
> > > CONFIG_CPU_THERMAL was enabled, then the soctherm driver would
> > > never be able to probe.
> >
> > Yes, this is a potential issue. However, this option in
> > tegra_defconfig is by default disabled when thermal is enabled.
> Not everybody uses tegra_defconfig for their kernel builds. In fact
> I'd imagine that the majority of kernels use a variant of
> multi_v7_defconfig and therefore CPU_THERMAL might get enabled
> irrespective of any Tegra support.

I see your point.

> I think a better solution would be to add this check only when proper
> support for CPU frequency based cooling is added. That is, when a call
> to cpufreq_cooling_register() (or a variant thereof) is added.

For the above reason the code is only compiled in when user enable

> But while at it, why not make it so that cpufreq_cooling_register()
> detects if a cpufreq driver has been registered yet and propagate
> -EPROBE_DEFER if necessary?

cpufreq_cooling_register() may be a good place to add check for
deferred probe.

The problem with cpufreq_cooling_register() is that it may be called
late in the probe function (as it is done now in Exynos).

> Thierry

Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
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