From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thierry Reding <thierry.reding@gmail.com>
Subject: Re: [PATCH 5/8] thermal:cpu cooling:tegra: Provide deferred probing
 for tegra driver
Date: Mon, 17 Nov 2014 12:57:44 +0100
Message-ID: <20141117115743.GG25699@ulmo>
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To: Lukasz Majewski <l.majewski@samsung.com>
Cc: Mikko Perttunen <mikko.perttunen@kapsi.fi>, Eduardo Valentin <edubezval@gmail.com>, Zhang Rui <rui.zhang@intel.com>, Ezequiel Garcia <ezequiel.garcia@free-electrons.com>, Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>, Linux PM list <linux-pm@vger.kernel.org>, Vincenzo Frascino <vincenzo.frascino@st.com>, Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, Lukasz Majewski <l.majewski@majess.pl>, Nobuhiro Iwamatsu <iwamatsu@nigauri.org>, Mikko Perttunen <mperttunen@nvidia.com>, Stephen Warren <swarren@wwwdotorg.org>, Alexandre Courbot <gnurou@gmail.com>, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org
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On Fri, Nov 14, 2014 at 12:24:37PM +0100, Lukasz Majewski wrote:
> Hi Mikko,
>=20
> > Tested-by: Mikko Perttunen <mikko.perttunen@kapsi.fi>
>=20
> Thanks for testing.
>=20
> >=20
> > One potential issue I can see is that if the cpufreq driver fails to=20
> > probe then you'll never get the thermal driver either. For example,=20
> > Tegra124 currently has no cpufreq driver, so if CONFIG_CPU_THERMAL
> > was enabled, then the soctherm driver would never be able to probe.
>=20
> 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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