linux-kernel - Re: [RFC] clk: qcom: common: Detach the power domain at the end of probe

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Message-ID: <20220926162324.xsh4niaxdmh3ao3i@builder.lan>
Date:   Mon, 26 Sep 2022 11:23:24 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Abel Vesa <abel.vesa@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] clk: qcom: common: Detach the power domain at the end of
 probe

On Thu, Aug 04, 2022 at 05:37:48PM +0300, Dmitry Baryshkov wrote:
> On Thu, 4 Aug 2022 at 13:35, Abel Vesa <abel.vesa@...aro.org> wrote:
> >
> > None of the CCs actually need the PD attached to their device,
> > but rather some GDSCs registered by those CCs need that PD as a parent
> > in order to propagate power gating and the performance state.
> >
> > So lets detach the PD from the CC right at the end of probe, after
> > everything has been successfully set up.
> 
> Would it still be possible to read the clock registers if we detach
> the device from the domain?
> I think it was the original issue behind putting the dispcc/videocc
> into the MMCX domain: to be able to poke into the clock registers,
> which are gated by the MMCX.
> 

I share the understanding, that on several modern platforms e.g. dispcc
was shown to depend on mmcx and the associated gcc abh clock being
enabled.

@Abel, could you please verify this on 8250/8350/8450?

Regards,
Bjorn

> 
> > Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> 
> 
> -- 
> With best wishes
> Dmitry