Message-ID: <CAPDyKFpJU3g2OzJeR9KUdtN-8wJsDckqVAMQMHBV=enu=DfURg@mail.gmail.com>
Date:   Mon, 6 Sep 2021 12:53:07 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephan Gerhold <stephan@...hold.net>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] PM: domains: Add a ->dev_get_performance_state()
 callback to genpd

On Sun, 5 Sept 2021 at 11:11, Dmitry Osipenko <digetx@...il.com> wrote:
>
> 03.09.2021 17:09, Ulf Hansson пишет:
> > On Fri, 3 Sept 2021 at 12:06, Dmitry Osipenko <digetx@...il.com> wrote:
> >>
> >> 03.09.2021 11:55, Ulf Hansson пишет:
> >>> On Fri, 3 Sept 2021 at 08:00, Dmitry Osipenko <digetx@...il.com> 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@...aro.org>
> >>>>> ---
> >>>>>  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.
>
> It's not clear to me whether you omitted handling the case of
> rpm-suspended device on purpose or not. I think it should be a part of
> this patch, but sounds like you want to work on it separately, correct?

I didn't omit the handling, but instead relied solely on the
pm_runtime_suspended() check in dev_pm_genpd_set_performance_state().

>
> >>>> 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?
>
> The current behaviour is incorrect for Tegra because it needs to set the
> rpm_pstate for rpm-suspended device, instead of bumping the state
> immediately.
>
> Power management is defeated without it on Tegra because SoC will start
> to consume extra power while device that needs this power is suspended.

Okay, I understand your concern.

For devices that may remain runtime suspended when their consumer
drivers probes them, the behaviour may be suboptimal. This because it
could lead to having an active performance state vote for a runtime
suspended device, at least until it gets runtime resumed and then
runtime suspended again.

This all boils down to how the consumer driver deploys support for
runtime PM - and genpd doesn't know nor can control that.

I wonder if we perhaps should just leave this as is then. In other
words, rely on the consumer driver to vote for an initial performance
state of the device during ->probe(). In this way, the consumer driver
can decide what is the best thing to do, rather than letting genpd
make guesses.

Note that, comparing what we have done for power on/off during
attach/probe. For the legacy case (the single PM domain case) we power
on the PM domain. For the multiple PM domain case, we leave the PM
domain as is.

>
> Otherwise $subject looks okay.
>
> > 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?
>
> Either is fine. Although, won't it be easier to keep these PD patches
> within the Tegra series since it depends on them? I can pick up the
> patches into the next version of Tegra series.

Let's see. If we can agree on how to deal with this series, maybe we
can ask Rafael to send another pull-request before rc1 is out, so you
can base your series for Tegra more easily on top.

Kind regards
Uffe

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