Re: [RESEND PATCH v2 4/7] clk: qcom: gdsc: enable optional power domain support

[Dmitry Baryshkov]

On Fri, 9 Jul 2021 at 15:18, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Fri, 9 Jul 2021 at 13:46, Dmitry Baryshkov
> <dmitry.baryshkov@xxxxxxxxxx> wrote:
> >
> > On Fri, 9 Jul 2021 at 12:33, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> > >
> > > On Fri, 9 Jul 2021 at 06:32, Dmitry Baryshkov
> > > <dmitry.baryshkov@xxxxxxxxxx> wrote:
> > > >
> > > > On sm8250 dispcc and videocc registers are powered up by the MMCX power
> > > > domain. Currently we used a regulator to enable this domain on demand,
> > > > however this has some consequences, as genpd code is not reentrant.
> > > >
> > > > Teach Qualcomm clock controller code about setting up power domains and
> > > > using them for gdsc control.
> > > >
> > > > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > >
> > > [...]
> > >
> > > > diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
> > > > index 51ed640e527b..9401d01533c8 100644
> > > > --- a/drivers/clk/qcom/gdsc.c
> > > > +++ b/drivers/clk/qcom/gdsc.c
> > > > @@ -427,6 +427,7 @@ int gdsc_register(struct gdsc_desc *desc,
> > > >                         continue;
> > > >                 scs[i]->regmap = regmap;
> > > >                 scs[i]->rcdev = rcdev;
> > > > +               scs[i]->pd.dev.parent = desc->dev;
> > > >                 ret = gdsc_init(scs[i]);
> > > >                 if (ret)
> > > >                         return ret;
> > > > @@ -439,6 +440,8 @@ int gdsc_register(struct gdsc_desc *desc,
> > > >                         continue;
> > > >                 if (scs[i]->parent)
> > > >                         pm_genpd_add_subdomain(scs[i]->parent, &scs[i]->pd);
> > > > +               else if (!IS_ERR_OR_NULL(dev->pm_domain))
> > >
> > > So dev_pm_domain_attach() (which calls genpd_dev_pm_attach() is being
> > > called for gdsc platform device from the platform bus', to try to
> > > attach the device to its corresponding PM domain.
> > >
> > > Looking a bit closer to genpd_dev_pm_attach(), I realize that we
> > > shouldn't really try to attach a device to its PM domain, when its OF
> > > node (dev->of_node) contains a "#power-domain-cells" specifier. This
> > > is because it indicates that the device belongs to a genpd provider
> > > itself. In this case, a "power-domains" specifier tells that it has a
> > > parent domain.
> > >
> > > I will post a patch that fixes this asap.
> >
> > I think there is nothing to fix here. The dispcc/videocc drivers
> > provide clocks in addition to the gdsc power domain. And provided
> > clocks would definitely benefit from having the dispcc device being
> > attached to the power domain which governs clock registers (MMCX in
> > our case). Thus I think it is perfectly valid to have:
> >
> > rpmhpd device:
> >  - provides MMCX domain.
> >
> > dispcc device:
> >  - is attached to the MMCX domain,
>
> We don't need this, it's redundant and weird to me.
>
> Also I am kind of worried that you will hit another new path in genpd,
> causing locking issues etc, as it has not been designed to work like
> this (a provider device and a child domain sharing the same "parent").

So, which domain should the dispcc device belong to? It's registers
are powered by the MMCX domain. I can not attach it to the child
(GDSC) domain either: in the case of videocc there are 4 child
domains.
An alternative would be to request that all users of the provided
clocks power on one of the child domains. However this is also not
perfect. If some generic code (e.g. clock framework) calls into
provided clocks (e.g. because of assigned-clock-rates), this can
happen w/o proper power domain being powered up yet.

>
> >  - provides MDSS_GDSC
>
> It's perfectly fine that dispcc acts as a genpd provider. In this
> case, the corresponding PM domain should be assigned as a child for
> the parent MMCX domain. That should make this work, I think.
>
> >  - provides clocks
>
> That sounds reasonable as well.
>
> >
> > >
> > > > +                       pm_genpd_add_subdomain(pd_to_genpd(dev->pm_domain), &scs[i]->pd);
> > > >         }
> > > >
> > > >         return of_genpd_add_provider_onecell(dev->of_node, data);
> > > > @@ -457,6 +460,8 @@ void gdsc_unregister(struct gdsc_desc *desc)
> > > >                         continue;
> > > >                 if (scs[i]->parent)
> > > >                         pm_genpd_remove_subdomain(scs[i]->parent, &scs[i]->pd);
> > > > +               else if (!IS_ERR_OR_NULL(dev->pm_domain))
> > >
> > > Ditto.
> > >
> > > > +                       pm_genpd_remove_subdomain(pd_to_genpd(dev->pm_domain), &scs[i]->pd);
> > > >         }
> > > >         of_genpd_del_provider(dev->of_node);
> > > >  }
> > > > --
> > > > 2.30.2
> > > >
> > >
>
> Kind regards
> Uffe



-- 
With best wishes
Dmitry