Re: [PATCH 3/3] PM: domains: Add a ->dev_get_performance_state() callback to genpd

[Ulf Hansson]

On Fri, 3 Sept 2021 at 08:00, Dmitry Osipenko <digetx@xxxxxxxxx> wrote:
>
> 02.09.2021 13:16, Ulf Hansson пишет:
> > Hardware may be preprogrammed to a specific performance state, which may
> > not be zero initially during boot. This may lead to that genpd's current
> > performance state becomes inconsistent with the state of the hardware. To
> > deal with this, the driver for a device that is being attached to its
> > genpd, need to request an initial performance state vote, which is
> > typically done by calling some of the OPP APIs while probing.
> >
> > In some cases this would lead to boilerplate code in the drivers. Let's
> > make it possible to avoid this, by adding a new optional callback to genpd
> > and invoke it per device during the attach process. In this way, the genpd
> > provider driver can inform genpd about the initial performance state that
> > is needed for the device.
> >
> > Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> > ---
> >  drivers/base/power/domain.c | 8 +++++---
> >  include/linux/pm_domain.h   | 2 ++
> >  2 files changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> > index 800adf831cae..1a6f3538af8d 100644
> > --- a/drivers/base/power/domain.c
> > +++ b/drivers/base/power/domain.c
> > @@ -2640,13 +2640,15 @@ static void genpd_dev_pm_sync(struct device *dev)
> >       genpd_queue_power_off_work(pd);
> >  }
> >
> > -static int genpd_get_default_performance_state(struct device *dev,
> > +static int genpd_get_default_performance_state(struct generic_pm_domain *genpd,
> > +                                            struct device *dev,
> >                                              unsigned int index)
> >  {
> >       int pstate = of_get_required_opp_performance_state(dev->of_node, index);
> >
> >       if (pstate == -ENODEV || pstate == -EOPNOTSUPP)
> > -             return 0;
> > +             pstate = genpd->dev_get_performance_state ?
> > +                      genpd->dev_get_performance_state(genpd, dev) : 0;
> >
> >       return pstate;
> >  }
> > @@ -2701,7 +2703,7 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
> >       }
> >
> >       /* Set the default performance state */
> > -     pstate = genpd_get_default_performance_state(dev, index);
> > +     pstate = genpd_get_default_performance_state(pd, dev, index);
>
> If base device is suspended, then its performance state is zero.
>
> When device will be rpm-resumed, then its performance should be set to
> the default state.
>
> You're setting performance state of the wrong device, it should be the
> base device and not the virtual domain device.

No I am not. :-) Let me elaborate.

For the single PM domain case, 'dev' and 'base_dev' are pointing to
the same device. So this works fine.

For the multiple PM domain case or when attaching goes via
genpd_dev_pm_attach_by_id(), 'dev' is the virtual device registered in
genpd_dev_pm_attach_by_id(). In this case, it's 'dev' that is becoming
attached to genpd and not the 'base_dev'. Note also that, runtime PM
has not been enabled for 'dev' yet at this point and 'dev' has been
assigned the same OF node as 'base_dev", to allow OF parsing to work
as is for it.

Moreover, to deal with runtime PM in the multiple PM domain case, the
consumer driver should create a device link. Along the lines of this:
device_link_add(base_dev, dev, DL_FLAG_PM_RUNTIME |
DL_FLAG_STATELESS), thus assigning the virtual device ('dev') as the
supplier for its consumer device ('base_dev').

>
> These all is handled properly by my patch [1]. Hence it's complicated
> for the reason.

See above. It shouldn't have to be complicated. If it still is, there
is something to fix for the multiple PM domain case.

>
> [1]
> https://patchwork.ozlabs.org/project/linux-tegra/patch/20210831135450.26070-5-digetx@xxxxxxxxx/

Kind regards
Uffe