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

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Message-ID: <20210818091417.dvlnsxlgybdsn76x@vireshk-i7>
Date:   Wed, 18 Aug 2021 14:44:17 +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>,
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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 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..

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.

> 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.

-- 
viresh