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

[Ulf Hansson]

On Thu, 3 Jun 2021 at 11:55, Viresh Kumar <viresh.kumar@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >
> > 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.

>
> > +             genpd_set_performance_state(dev, state);
> > +}
> > +
> >  /**
> >   * dev_pm_genpd_set_performance_state- Set performance state of device's power
> >   * domain.
> > @@ -842,7 +859,8 @@ static int genpd_runtime_suspend(struct device *dev)
> >  {
> >       struct generic_pm_domain *genpd;
> >       bool (*suspend_ok)(struct device *__dev);
> > -     struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
> > +     struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
> > +     struct gpd_timing_data *td = &gpd_data->td;
> >       bool runtime_pm = pm_runtime_enabled(dev);
> >       ktime_t time_start;
> >       s64 elapsed_ns;
> > @@ -899,6 +917,7 @@ static int genpd_runtime_suspend(struct device *dev)
> >               return 0;
> >
> >       genpd_lock(genpd);
> > +     gpd_data->rpm_pstate = genpd_drop_performance_state(dev);
>
> So this will become:
>
>         genpd_drop_performance_state(dev, &gpd_data->rpm_pstate);
>
> and it can have return type of void.

See more above, about the reason why it looks like this. Hopefully
that explains it.

Kind regards
Uffe