linux-kernel - Re: [PATCH v8 01/34] opp: Add dev_pm_opp

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Date:   Wed, 18 Aug 2021 15:20:44 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-staging@...ts.linux.dev, linux-spi@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v8 01/34] opp: Add dev_pm_opp_sync() helper

On 18-08-21, 11:41, Ulf Hansson wrote:
> On Wed, 18 Aug 2021 at 11:14, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > What we need here is just configure. So something like this then:
> >
> > - genpd->get_performance_state()
> >   -> dev_pm_opp_get_current_opp() //New API
> >   -> dev_pm_genpd_set_performance_state(dev, current_opp->pstate);
> >
> > This can be done just once from probe() then.
> 
> How would dev_pm_opp_get_current_opp() work? Do you have a suggestion?

The opp core already has a way of finding current OPP, that's what
Dmitry is trying to use here. It finds it using clk_get_rate(), if
that is zero, it picks the lowest freq possible.

> I am sure I understand the problem. When a device is getting probed,
> it needs to consume power, how else can the corresponding driver
> successfully probe it?

Dmitry can answer that better, but a device doesn't necessarily need
to consume energy in probe. It can consume bus clock, like APB we
have, but the more energy consuming stuff can be left disabled until
the time a user comes up. Probe will just end up registering the
driver and initializing it.

-- 
viresh