linux-kernel - Re: [PATCH v5 3/3] thermal: cpu_cooling: Migrate to using the EM framework

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Message-ID: <20190530112747.nlfyctzjkz5lak7o@queper01-lin>
Date:   Thu, 30 May 2019 12:27:49 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     edubezval@...il.com, rui.zhang@...el.com, javi.merino@...nel.org,
        viresh.kumar@...aro.org, amit.kachhap@...il.com, rjw@...ysocki.net,
        will.deacon@....com, catalin.marinas@....com,
        daniel.lezcano@...aro.org, dietmar.eggemann@....com,
        ionela.voinescu@....com, mka@...omium.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 3/3] thermal: cpu_cooling: Migrate to using the EM
 framework

On Thursday 30 May 2019 at 10:20:38 (+0100), Quentin Perret wrote:
> The newly introduced Energy Model framework manages power cost tables in
> a generic way. Moreover, it supports several types of models since the
> tables can come from DT or firmware (through SCMI) for example. On the
> other hand, the cpu_cooling subsystem manages its own power cost tables
> using only DT data.
> 
> In order to avoid the duplication of data in the kernel, and in order to
> enable IPA with EMs coming from more than just DT, remove the private
> tables from cpu_cooling.c and migrate it to using the centralized EM
> framework. Doing so should have no visible functional impact for
> existing users of IPA since:
> 
>  - recent extenstions to the the PM_OPP infrastructure enable the
>    registration of EMs in PM_EM using the DT property used by IPA;
> 
>  - the existing upstream cpufreq drivers marked with the
>    'CPUFREQ_IS_COOLING_DEV' flag all use the aforementioned PM_OPP
>    infrastructure, which means they all support PM_EM. The only two
>    exceptions are qoriq-cpufreq which doesn't in fact use an EM and
>    scmi-cpufreq which doesn't use DT for power costs.
> 
> For existing users of cpu_cooling, PM_EM tables will contain the exact
> same power values that IPA used to compute on its own until now. The
> only new dependency for them is to compile in CONFIG_ENERGY_MODEL.
> 
> The case where the thermal subsystem is used without an Energy Model
> (cpufreq_cooling_ops) is handled by looking directly at CPUFreq's
> frequency table which is already a dependency for cpu_cooling.c anyway.
> Since the thermal framework expects the cooling states in a particular
> order, bail out whenever the CPUFreq table is unsorted, since that is
> fairly uncommon in general, and there are currently no users of
> cpu_cooling for this use-case.
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Viresh: the patch hasn't changed much so I kept this, but please shout
if you're not happy with the new version :-)

Thanks,
Quentin