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

Thierry Reding
2014-11-17T11:57:49Z

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On Fri, Nov 14, 2014 at 12:24:37PM +0100, Lukasz Majewski wrote:
> Hi Mikko,
>
> > Tested-by: Mikko Perttunen <mikko.perttunen@kapsi.fi>
>
> 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 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.

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?

Thierry

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