Re: [PATCH 0/8] cpufreq: Auto-register with energy model

From: Quentin Perret <qperret@google.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Rafael Wysocki <rjw@rjwysocki.net>,
	Vincent Donnefort <vincent.donnefort@arm.com>,
	lukasz.luba@arm.com, Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Cristian Marussi <cristian.marussi@arm.com>,
	Fabio Estevam <festevam@gmail.com>,
	Kevin Hilman <khilman@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Shawn Guo <shawnguo@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	linux-pm@vger.kernel.org,
	Vincent Guittot <vincent.guittot@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mediatek@lists.infradead.org, linux-omap@vger.kernel.org
Subject: Re: [PATCH 0/8] cpufreq: Auto-register with energy model
Date: Wed, 11 Aug 2021 11:12:47 +0100	[thread overview]
Message-ID: <YROin5WudmmEPard@google.com> (raw)
In-Reply-To: <20210811095311.e6wnma2ubkqdtuic@vireshk-i7>

On Wednesday 11 Aug 2021 at 15:23:11 (+0530), Viresh Kumar wrote:
> On 11-08-21, 10:48, Quentin Perret wrote:
> > I think this should work, but perhaps will be a bit tricky for cpufreq
> > driver developers as they need to have a pretty good understanding of
> > the stack to know that they should do the registration from here and not
> > ->init() for instance. Suggested alternative: we introduce a ->register_em()
> > callback to cpufreq_driver, and turn dev_pm_opp_of_register_em() into a
> > valid handler for this callback. This should 'document' things a bit
> > better, avoid some of the problems your other series tried to achieve, and
> > allow us to call the EM registration in exactly the right place from
> > cpufreq core. On the plus side, we could easily make this work for e.g.
> > the SCMI driver which would only need to provide its own version of
> > ->register_em().
> > 
> > Thoughts?
> 
> I had exactly the same thing in mind, but was thinking of two
> callbacks, to register and unregister. But yeah, we aren't going to
> register for now at least :)

Ack, we probably want both once we unregister things.

> I wasn't sure if that should be done or not, since we also have
> ready() callback. So was reluctant to suggest it earlier. But that can
> work well as well.

I think using the ready() callback can work just fine as long as we
document clearly it is important to register the EM from there and not
anywhere else. The dedicated em_register() callback makes that a bit
clearer and should avoid a bit of boilerplate in the driver, but it's
not a big deal really, so I'm happy either way ;)