linux-kernel - Re: [PATCH v13 13/35] drm/tegra: gr2d: Support generic power domain and runtime PM

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Date:   Fri, 1 Oct 2021 16:55:11 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
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 13/35] drm/tegra: gr2d: Support generic power domain
 and runtime PM

On Fri, 1 Oct 2021 at 16:29, Dmitry Osipenko <digetx@...il.com> wrote:
>
> 01.10.2021 16:39, Ulf Hansson пишет:
> > On Mon, 27 Sept 2021 at 00:42, Dmitry Osipenko <digetx@...il.com> wrote:
> >>
> >> Add runtime power management and support generic power domains.
> >>
> >> Tested-by: Peter Geis <pgwipeout@...il.com> # Ouya T30
> >> Tested-by: Paul Fertser <fercerpav@...il.com> # PAZ00 T20
> >> Tested-by: Nicolas Chauvet <kwizart@...il.com> # PAZ00 T20 and TK1 T124
> >> Tested-by: Matt Merhar <mattmerhar@...tonmail.com> # Ouya T30
> >> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> >> ---
> >>  drivers/gpu/drm/tegra/gr2d.c | 155 +++++++++++++++++++++++++++++++++--
> >
> > [...]
> >
> >>  static int gr2d_remove(struct platform_device *pdev)
> >> @@ -259,15 +312,101 @@ static int gr2d_remove(struct platform_device *pdev)
> >>                 return err;
> >>         }
> >>
> >> +       pm_runtime_dont_use_autosuspend(&pdev->dev);
> >> +       pm_runtime_disable(&pdev->dev);
> >
> > There is no guarantee that the ->runtime_suspend() has been invoked
> > here, which means that clock may be left prepared/enabled beyond this
> > point.
> >
> > I suggest you call pm_runtime_force_suspend(), instead of
> > pm_runtime_disable(), to make sure that gets done.
>
> The pm_runtime_disable() performs the final synchronization, please see [1].
>
> [1]
> https://elixir.bootlin.com/linux/v5.15-rc3/source/drivers/base/power/runtime.c#L1412

pm_runtime_disable() end up calling _pm_runtime_barrier(), which calls
cancel_work_sync() if dev->power.request_pending has been set.

If the work that was punted to the pm_wq in rpm_idle() has not been
started yet, we end up just canceling it. In other words, there are no
guarantees it runs to completion.

Moreover, use space may have bumped the usage count via sysfs for the
device (pm_runtime_forbid()) to keep the device runtime resumed.

>
> Calling pm_runtime_force_suspend() isn't correct because each 'enable'
> must have the corresponding 'disable'. Hence there is no problem here.

pm_runtime_force_suspend() calls pm_runtime_disable(), so I think that
should be fine. No?

Kind regards
Uffe