linux-kernel - Re: [PATCH] clk: qcom: gdsc: Remove direct runtime PM calls

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Message-ID: <20221102024927.n5mjyzyqyapveapa@builder.lan>
Date:   Tue, 1 Nov 2022 21:49:27 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, patches@...ts.linux.dev,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        linux-arm-msm@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Johan Hovold <johan+linaro@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Taniya Das <quic_tdas@...cinc.com>,
        Satya Priya <quic_c_skakit@...cinc.com>,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH] clk: qcom: gdsc: Remove direct runtime PM calls

On Tue, Nov 01, 2022 at 04:34:21PM -0700, Stephen Boyd wrote:
> We shouldn't be calling runtime PM APIs from within the genpd
> enable/disable path for a couple reasons.
[..][
> Upon closer inspection, calling runtime PM APIs like this in the GDSC
> driver doesn't make sense. It was intended to make sure the GDSC for the
> clock controller providing other GDSCs was enabled, specifically the
> MMCX GDSC for the display clk controller on SM8250 (sm8250-dispcc), so
> that GDSC register accesses succeeded. That will already happen because
> we make the 'dev->pm_domain' a parent domain of each GDSC we register in
> gdsc_register() via pm_genpd_add_subdomain(). When any of these GDSCs
> are accessed, we'll enable the parent domain (in this specific case
> MMCX).
> 

It's correct that adding the GDSCs as subdomains for the device's
parent-domain will ensure that enabling a GDSC will propagate up and
turn on the (typically) rpmhpd resource.

But the purpose for the explicit calls was to ensure that the clock
controller itself is accessible. It's been a while since I looked at
this, but iirc letting MMCX to turn off would cause the register access
during dispcc probing to fail - similar to how
clk_pm_runtime_get()/put() ensures the clock registers are accessible.


Perhaps I misunderstood something in the process, or lost track of the
actual issues?

Regards,
Bjorn