linux-kernel - Re: [PATCH 2/3] PM: domains: Drop/restore performance state votes for devices at runtime PM

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Message-ID: <CAPDyKFoodEvWCm17=+4NV3snHpSP4qbOzz4+PFyjc=UHvQysOQ@mail.gmail.com>
Date:   Thu, 3 Jun 2021 11:16:16 +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 2/3] PM: domains: Drop/restore performance state votes for
 devices at runtime PM

On Thu, 3 Jun 2021 at 04:37, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 03-06-21, 08:04, Viresh Kumar wrote:
> > On 02-06-21, 12:12, 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>
> > > ---
> > >  drivers/base/power/domain.c | 21 +++++++++++++++++++--
> > >  include/linux/pm_domain.h   |  1 +
> > >  2 files changed, 20 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> > > index a3b6e751f366..81b9d4652b90 100644
> > > --- a/drivers/base/power/domain.c
> > > +++ b/drivers/base/power/domain.c
> > > @@ -397,6 +397,18 @@ static int genpd_set_performance_state(struct device *dev, unsigned int state)
> > >     return ret;
> > >  }
> > >
> > > +static int genpd_drop_performance_state(struct device *dev)
> > > +{
> > > +   struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
> > > +   unsigned int prev_state;
> > > +
> > > +   prev_state = gpd_data->performance_state;
> > > +   if (prev_state && !genpd_set_performance_state(dev, 0))
> >
> > What about adding this prev_state check in
> > genpd_set_performance_state() itself ? We already have one for the
> > genpd in _genpd_set_performance_state(), why not one for the device ?
> >
> > > +           return prev_state;
> > > +
> > > +   return 0;
> >
> > Hmm, we will return 0 in case genpd_set_performance_state() fails,
> > which will make us set the state to 0 again on resume. Maybe add a
> > comment for this somewhere ?
>
> No, we won't as you check for rpm_saved_pstate there, so the device
> will stay disabled.
>
> Again adding the check into genpd_set_performance_state() may help
> reducing similar checks elsewhere.

Yes, at closer look, I think it makes sense to me as well.

Although, as it means a change in behaviour, I decided to make it a
separate patch. Let me respin the series to fold it in.

[...]

Thanks for reviewing!

Kind regards
Uffe