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

[Ulf Hansson]

On Fri, 3 Sept 2021 at 12:06, Dmitry Osipenko <digetx@xxxxxxxxx> wrote:
>
> 03.09.2021 11:55, Ulf Hansson пишет:
> > 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
> Are you okay with my variant of handling the suspended device?

Not sure if you intended to post this line?

In any case, I am happy to help and review to move things forward.

>
>
> >> 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]
> Alright, it actually works now on Tegra using the dev in the callback
> for the case of multiple domains, I re-checked it. Previously, when I
> tried that, there was a conflict in regards to OPP usage, I don't
> remember details anymore. Maybe the recent changes that were suggested
> by Viresh helped with that. So yes, there is no need to pass the base
> device anymore.

Great! So, it seems like $subject patch should be a way forward for you then?

BTW, I forgot to add your Suggested-by: tag for the patch, you
certainly deserve at least that. Or perhaps you are fine with
co-developed by tag?

Kind regards
Uffe