linux-kernel - Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain

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Date:   Thu, 7 Oct 2021 00:25:05 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     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>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Nishanth Menon <nm@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        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-pwm@...r.kernel.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        David Heidelberg <david@...t.cz>
Subject: Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain

06.10.2021 15:38, Ulf Hansson пишет:
>> I'm also wondering if we could add some 'was_enabled' flag to GENPDs,
>> setting it by genpd_suspend_noirq() for the enabled domains, and then
>> powering-on GENPDs from genpd_resume_noirq() only if they were in the
>> enabled state during genpd_suspend_noirq() time. It actually puzzled me
>> for a quite long time why GENPD core enables domains unconditionally
>> during early resume. This should solve a part of the problem and it
>> makes suspend/resume a bit safer because there is a smaller chance to
>> crash hardware during suspend, at least it's easier to debug.
> Just because the PM domain was already off at genpd_suspend_noirq(),
> doesn't mean that it can stay powered off at genpd_resume_noirq(). At
> least as is today.
> 
> The main reason why genpd_resume_noirq() powers on the PM domain, is
> because it's not possible for the consumer drivers to rely on runtime
> PM to do it (because runtime PM has been disabled by the PM core).

At least Tegra doesn't need to have domains force-resumed. This should
be a platform-specific behaviour. We may add a new flag for that, I
suppose. I'll try to keep this in mind for a future improvement. Thank
you for the clarification.