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

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Message-ID: <CAPDyKFrVxhrWGr2pKduehshpLFd_db2NTPGuD7fSqvuHeyzT4w@mail.gmail.com>
Date:   Wed, 18 Aug 2021 11:41:26 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Viresh Kumar <viresh.kumar@...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,
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        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 Wed, 18 Aug 2021 at 11:14, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 18-08-21, 10:29, Ulf Hansson wrote:
> > Me and Dmitry discussed adding a new genpd callback for this. I agreed
> > that it seems like a reasonable thing to add, if he insists.
> >
> > The intent was to invoke the new callback from __genpd_dev_pm_attach()
> > when the device has been attached to its genpd. This allows the
> > callback, to invoke clk_get_rate() and then dev_pm_opp_set_rate(), to
> > update the vote according to the current state of the HW.
>
> I wouldn't call dev_pm_opp_set_rate() from there, since it means
> configure and enable (both) for different resources, clk, regulator,
> genpd, etc..

Right, good point!

dev_pm_opp_set_rate() is best called from consumer drivers, as they
need to be in control.

>
> 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?

>
> > I am not sure if/why that approach seemed insufficient?
> >
> > Another option to solve the problem, I think, is simply to patch
> > drivers to let them call dev_pm_opp_set_rate() during ->probe(), this
> > should synchronize the HW state too.
>
> Dmitry already mentioned that this will make the device start
> consuming power, and he doesn't want that, else we need an explicit
> disble call as well.

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?

>
> --
> viresh

Kind regards
Uffe