Re: [PATCH v2 3/4] PM: domains: Drop/restore performance state votes for devices at runtime PM

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Linux PM <linux-pm@vger.kernel.org>,
	Dmitry Osipenko <digetx@gmail.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	Rajendra Nayak <rnayak@codeaurora.org>,
	Stephan Gerhold <stephan@gerhold.net>,
	Roja Rani Yarubandi <rojay@codeaurora.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Stephen Boyd <sboyd@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 3/4] PM: domains: Drop/restore performance state votes for devices at runtime PM
Date: Wed, 9 Jun 2021 14:25:21 +0200	[thread overview]
Message-ID: <CAPDyKFrQWUWsuEn6NfT5zjXbSDArgmceW=JpKNwwH2Rm19=iXw@mail.gmail.com> (raw)
In-Reply-To: <20210607044738.3aec6o4imq6u3x6e@vireshk-i7>

On Mon, 7 Jun 2021 at 06:47, Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 04-06-21, 09:45, Ulf Hansson wrote:
> > Starting calls from the subsystem/driver:
> >
> > ------
> > dev_pm_genpd_set_performance_state(dev, 100);
> > "run a use case with device runtime resumed"
> > ...
> > "use case ends"
> > dev_pm_genpd_set_performance_state(dev, 0);
> > pm_runtime_put()
> >     ->genpd_runtime_suspend()
> >     gpd_data->performance_state == 0, -> gpd_data->rpm_pstate = 0;
> > ...
> > "new use case start"
> > dev_pm_genpd_set_performance_state(dev, 100);
> > pm_runtime_get_sync()
> >     ->genpd_runtime_resume()
> >     gpd_data->performance_state == 100, -> gpd_data->rpm_pstate = 0;
> > (This is where we need to check for "zero" to not override the value)
> > .....
> > ------
> >
> > I wouldn't say that the above is the way how I see the calls to
> > dev_pm_genpd_set_performance_state (or actually
> > dev_pm_opp_set_rate|opp()) being deployed. The calls should rather be
> > done from the subsystem/driver's ->runtime_suspend|resume() callback,
> > then the path above would work in the way you suggest.
> >
> > Although, as we currently treat performance states and power states in
> > genpd orthogonally, I wanted to make sure we could cope with both
> > situations.
>
> I think letting the drivers to call
> dev_pm_genpd_set_performance_state(dev, 0) from suspend/resume makes
> it really ugly/racy as both depend on the gpd_data->performance_state
> for this. It doesn't look nice. And we shouldn't try to protect such
> drivers.
>
> Anyway, your call :)

Well, I am not sure we have an option at this point. As long as we
allow performance states to be managed orthogonally to on/off states
in genpd, the check in genpd_restore_performance_state() is needed.

I have started to prepare a new version of the series - and will add a
comment about this in the code to try to clarify this.

[...]

Kind regards
Uffe