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

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Date:   Tue, 29 Jun 2021 10:09:31 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Ulf Hansson <ulf.hansson@...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 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.

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