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

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Date:	Mon, 17 Nov 2014 13:51:42 +0100
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Mikko Perttunen <mikko.perttunen@...si.fi>,
	Eduardo Valentin <edubezval@...il.com>,
	Zhang Rui <rui.zhang@...el.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Vincenzo Frascino <vincenzo.frascino@...com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Nobuhiro Iwamatsu <iwamatsu@...auri.org>,
	Mikko Perttunen <mperttunen@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] thermal:cpu cooling:tegra: Provide deferred probing
 for tegra driver

Hi Thierry,

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

> 
> 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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