linux-kernel - Re: [PATCH 15/15] arm64: dts: qcom: sm6115: Add VDD_CX to GPU

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Message-ID: <ZLZ94Qc6x1HyjJPQ@gerhold.net>
Date:   Tue, 18 Jul 2023 13:56:45 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 15/15] arm64: dts: qcom: sm6115: Add VDD_CX to GPU_CCC

On Mon, Jul 17, 2023 at 09:18:21PM +0200, Konrad Dybcio wrote:
> On 17.07.2023 19:23, Stephan Gerhold wrote:
> > On Mon, Jul 17, 2023 at 07:11:33PM +0200, Konrad Dybcio wrote:
> >> On 17.07.2023 18:56, Stephan Gerhold wrote:
> >>> On Mon, Jul 17, 2023 at 06:50:18PM +0200, Konrad Dybcio wrote:
> >>>> On 17.07.2023 18:28, Stephan Gerhold wrote:
> >>>>> On Mon, Jul 17, 2023 at 05:19:22PM +0200, Konrad Dybcio wrote:
> >>>>>> The GPU_CC block is powered by VDD_CX. Describe that.
> >>>>>>
> >>>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> >>>>>> ---
> >>>>>>  arch/arm64/boot/dts/qcom/sm6115.dtsi | 2 ++
> >>>>>>  1 file changed, 2 insertions(+)
> >>>>>>
> >>>>>> diff --git a/arch/arm64/boot/dts/qcom/sm6115.dtsi b/arch/arm64/boot/dts/qcom/sm6115.dtsi
> >>>>>> index 29b5b388cd94..bfaaa1801a4d 100644
> >>>>>> --- a/arch/arm64/boot/dts/qcom/sm6115.dtsi
> >>>>>> +++ b/arch/arm64/boot/dts/qcom/sm6115.dtsi
> >>>>>> @@ -1430,6 +1430,8 @@ gpucc: clock-controller@...0000 {
> >>>>>>  			clocks = <&rpmcc RPM_SMD_XO_CLK_SRC>,
> >>>>>>  				 <&gcc GCC_GPU_GPLL0_CLK_SRC>,
> >>>>>>  				 <&gcc GCC_GPU_GPLL0_DIV_CLK_SRC>;
> >>>>>> +			power-domains = <&rpmpd SM6115_VDDCX>;
> >>>>>> +			required-opps = <&rpmpd_opp_low_svs>;
> >>>>>
> >>>>> Where is this required-opp coming from? The clocks in gpucc seem to have
> >>>>> different voltage requirements depending on the rates, but we usually
> >>>>> handle that in the OPP tables of the consumer.
> >>>> The only lower levels defined for this SoC are VDD_MIN and VDD_RET,
> >>>> but quite obviously the GPU won't work then
> >>>>
> >>>
> >>> The levels needed for the GPU clocks to run should be in the GPU OPP
> >>> table though, just like e.g. sdhc2_opp_table for the SDCC clocks.
> >>>
> >>> I still don't really understand why this is specified here. :)
> >> The GPU_CC block needs this rail to be at a certain power level for
> >> register access. This describes that requirement.
> >>
> > 
> > Can you show where this is defined downstream? On a quick look I didn't
> > see something like that anywhere. Or is this from some secret
> > documentation?
> As far as downstream goes, you can notice that no branch's or RCG's
> vdd tables ever define a level lower than the one I mentioned.
> 

As far as I can tell the vdd tables are only used when the clock is
actually enabled though, not for writing to registers while they are
disabled.

Stephan