linux-kernel - Re: [PATCH 2/2] PM: domain: use per-genpd lockdep class

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Message-ID: <CAPDyKFqSwPn7wUXB9mayT78hshDFBK+DO7cqbmZRjXNAJDQfZw@mail.gmail.com>
Date:   Thu, 1 Jul 2021 12:06:58 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>
Subject: Re: [PATCH 2/2] PM: domain: use per-genpd lockdep class

On Tue, 29 Jun 2021 at 17:09, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Mon 28 Jun 14:55 CDT 2021, Dmitry Baryshkov wrote:
>
> > Hi,
> >
> > On 17/06/2021 12:07, Ulf Hansson wrote:
> > > + Rajendra
> > >
> > > On Tue, 15 Jun 2021 at 17:55, Bjorn Andersson
> > > <bjorn.andersson@...aro.org> wrote:
> [..]
> > > > But I am unable to find a way for the gdsc driver to get hold of the
> > > > struct generic_pm_domain of the resources exposed by the rpmhpd driver.
> > >
> > > You don't need a handle to the struct generic_pm_domain, to assign a
> > > parent/child domain. Instead you can use of_genpd_add_subdomain(),
> > > which takes two "struct of_phandle_args*" corresponding to the
> > > parent/child device nodes of the genpd providers and then let genpd
> > > internally do the look up.
> >
> [..]
> >
> > I think I'd need this function anyway for the gdsc code. During gdsc_init()
> > we check gdsc status and this requires register access (and thus powering on
> > the parent domain) before the gdsc is registered itself as a power domain.
> >
>
> But this is a register access in the dispcc block, which is the context
> that our gdsc_init() operates. So describing that MMCX is the
> power-domain for dispcc should ensure that the power-domain is enabled.

Right.

As a note, when we assign a child domain to a parent domain, via
of_genpd_add_subdomain() for example - and the child domain has been
powered on, this requires the parent domain to be turned on as well.

>
> We do however need to make sure that dispcc doesn't hog its
> power-domain, and that any register accesses in runtime is done with the
> parenting power-domain enabled. E.g. the clock framework wraps all
> operations in pm_runtime_get/put(), but I don't see anything in the
> gnepd code for this.
>
>
> And for gcc I'm worried that we might have some GDSCs that are parented
> by CX and some by MX, but I do still think that the register accesses
> are only related to one of these.
>
> But this seems like a continuation of the special case in dispcc, so I
> think we should be able to focus on getting that right before we attempt
> the general case (and I don't know if we have a need for this today).
>
> Regards,
> Bjorn

Unfortunately, I didn't understand all the above things.

In any case, please tell me if there is anything else that blocks you
from moving forward with the power domain conversion? I am happy to
help.

Kind regards
Uffe