linux-kernel - Re: [PATCH v11 1/3] arm64: dts: qcom: sm8750: Add USB support to SM8750 SoCs

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Message-ID: <fe210f0b-692b-4c45-afc4-fc2bc5e57854@oss.qualcomm.com>
Date: Mon, 3 Nov 2025 20:40:32 +0530
From: Akhil P Oommen <akhilpo@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>,
        Krishna Kurapati <krishna.kurapati@....qualcomm.com>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Konrad Dybcio <konradybcio@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Wesley Cheng <wesley.cheng@....qualcomm.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v11 1/3] arm64: dts: qcom: sm8750: Add USB support to
 SM8750 SoCs

On 11/2/2025 9:23 PM, Bjorn Andersson wrote:
> On Sun, Nov 02, 2025 at 12:43:07AM +0530, Akhil P Oommen wrote:
>> On 11/1/2025 11:14 PM, Krishna Kurapati wrote:
>>> From: Wesley Cheng <wesley.cheng@....qualcomm.com>
>>> diff --git a/arch/arm64/boot/dts/qcom/sm8750.dtsi b/arch/arm64/boot/dts/qcom/sm8750.dtsi
> [..]
>>> +			power-domains = <&gcc GCC_USB30_PRIM_GDSC>;
>>> +			required-opps = <&rpmhpd_opp_nom>;
>>
>> Probably I am missing something, but which power domain associated to a
>> rail is scaled to NOM corner here?
>>
> 
> That would be the parent of the GCC_USB30_PRIM_GDSC, which should be the
> CX rail. We currently have a NOM requirement here just in case we're
> going to operate a SuperSpeed link, and the driver doesn't scale.
> 

This is a bit concerning. There are other subsystems which share CX
rail, including GPU. So a hw spec violation on USB may impact these
subsystems which would be pretty hard to root cause to USB.

@Krishna, do you plan to fix this with a follow up patch?

> 
> That said, your question is very much valid, because on SM8750 GCC
> doesn't specify CX as a power-domain of &gcc, this vote goes into the
> void.

So the fix is to just add the VDD_CX power domain to the gcc node and a
gcc driver change to enable "use_rpm" flag?

-Akhil

> 
> Regards,
> Bjorn