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

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Date:   Thu, 3 Jun 2021 13:17:18 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Dmitry Osipenko <digetx@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephan Gerhold <stephan@...hold.net>,
        Roja Rani Yarubandi <rojay@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] PM: domains: Drop/restore performance state votes
 for devices at runtime PM

On Thu, 3 Jun 2021 at 12:31, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Thu, 3 Jun 2021 at 11:55, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > On 03-06-21, 11:34, Ulf Hansson wrote:
> > > A subsystem/driver that need to manage OPPs for its device, should
> > > typically drop its vote for the OPP when the device becomes runtime
> > > suspended. In this way, the corresponding aggregation of the performance
> > > state votes that is managed in genpd for the attached PM domain, may find
> > > that the aggregated vote can be decreased. Hence, it may allow genpd to set
> > > the lower performance state for the PM domain, thus avoiding to waste
> > > energy.
> > >
> > > To accomplish this, typically a subsystem/driver would need to call
> > > dev_pm_opp_set_rate|opp() for its device from its ->runtime_suspend()
> > > callback, to drop the vote for the OPP. Accordingly, it needs another call
> > > to dev_pm_opp_set_rate|opp() to restore the vote for the OPP from its
> > > ->runtime_resume() callback.
> > >
> > > To avoid boilerplate code in subsystems/driver to deal with these things,
> > > let's instead manage this internally in genpd.
> > >
> > > Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> > > ---
> > >
> > > Changes in v2:
> > >       - Rebased.
> > >       - A few minor cosmetic changes.
> > >       - Deal with the error path in genpd_runtime_resume().
> > >
> > > ---
> > >  drivers/base/power/domain.c | 27 +++++++++++++++++++++++++--
> > >  include/linux/pm_domain.h   |  1 +
> > >  2 files changed, 26 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> > > index ef25a5b18587..e5d97174c254 100644
> > > --- a/drivers/base/power/domain.c
> > > +++ b/drivers/base/power/domain.c
> > > @@ -400,6 +400,23 @@ static int genpd_set_performance_state(struct device *dev, unsigned int state)
> > >       return ret;
> > >  }
> > >
> > > +static int genpd_drop_performance_state(struct device *dev)
> >
> > What about passing the state pointer here? that will simplify the
> > callers to just a call.
>
> Not sure I get that. Can you elaborate a bit more?
>
> >
> > > +{
> > > +     unsigned int prev_state = dev_gpd_data(dev)->performance_state;
> > > +
> > > +     if (!genpd_set_performance_state(dev, 0))
> > > +             return prev_state;
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +static void genpd_restore_performance_state(struct device *dev,
> > > +                                         unsigned int state)
> > > +{
> > > +     if (state)
> >
> > I will skip this check, as we are checking it in
> > genpd_set_performance_state() anyway ?
>
> I don't want us to override OPP votes made by the subsystem/driver
> level runtime PM callbacks. For example, if the drivers manage this
> thing themselves, that should be preserved.
>
> That said, by the check above I want to avoid setting the state to
> zero internally by genpd, if the driver level ->runtime_resume()
> callback has already restored the state.

Ehh, forget about what I said about the ->runtime_resume() callback.

I am mostly trying to avoid restoring a state that is zero, just to be
sure nobody else on some different level outside gendp, have decided
to set a new OPP in-between our calls to
genpd_drop|restore_performance state.

[...]

Kind regards
Uffe