Re: [PATCH v3 3/3] thermal: cpu_cooling: Migrate to using the EM framework

From: Eduardo Valentin <edubezval@gmail.com>
To: Quentin Perret <quentin.perret@arm.com>
Cc: linux-pm@vger.kernel.org, viresh.kumar@linaro.org,
	amit.kachhap@gmail.com, daniel.lezcano@linaro.org,
	rjw@rjwysocki.net, linux-kernel@vger.kernel.org,
	will.deacon@arm.com, mka@chromium.org, catalin.marinas@arm.com,
	rui.zhang@intel.com, javi.merino@kernel.org,
	ionela.voinescu@arm.com, dietmar.eggemann@arm.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 3/3] thermal: cpu_cooling: Migrate to using the EM framework
Date: Tue, 14 May 2019 07:17:37 -0700	[thread overview]
Message-ID: <20190514141736.GB16968@localhost.localdomain> (raw)
In-Reply-To: <20190514071506.ykjg67elsydaehlz@queper01-ThinkPad-T460s>

Hey Quentin,

On Tue, May 14, 2019 at 08:15:08AM +0100, Quentin Perret wrote:
> Hi Eduardo,
> 
> On Monday 13 May 2019 at 20:40:59 (-0700), Eduardo Valentin wrote:
> > On Fri, May 03, 2019 at 10:44:09AM +0100, Quentin Perret wrote:
> > > The newly introduced Energy Model framework manages power cost tables in
> > > a generic way. Moreover, it supports a 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.
> > > 
> > > 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.
> > 
> > Will this break DT in any way? After this change, are the existing DTs
> > still compatible with this cpu cooling?
> 
> Yes, all existing DTs stay compatible with this CPU cooling. The EM can
> still be built using the 'dynamic-power-coefficient' DT property thanks
> to the recently introduced dev_pm_opp_of_register_em() helper, see
> a4f342b9607d ("PM / OPP: Introduce a power estimation helper"). And all
> relevant cpufreq drivers have already been updated to use that function.

I see..

> 
> So, this patch should cause no functional change for all existing users.
> It's really just plumbing. I can probably explain that better in this
> commit message rather than the cover letter if you feel it is necessary.
> 

Yes I would prefer if this info goes into the commit message.

> Thanks,
> Quentin

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