linux-kernel - Re: [Patch v2] arm64: dts: qcom: sc7280: Add required-opps for USB

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Date:   Fri, 16 Sep 2022 12:42:00 +0000
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Rajendra Nayak <quic_rjendra@...cinc.com>
Cc:     agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...ainline.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        sboyd@...nel.org, johan+linaro@...nel.org,
        quic_kriskura@...cinc.com, dianders@...omium.org
Subject: Re: [Patch v2] arm64: dts: qcom: sc7280: Add required-opps for USB

On Fri, Sep 16, 2022 at 04:01:24PM +0530, Rajendra Nayak wrote:
> USB has a requirement to put a performance state vote on 'cx'
> while active. Use 'required-opps' to pass this information from
> device tree, and since all the GDSCs in GCC (including USB) are
> sub-domains of cx, we also add cx as a power-domain for GCC.
> Now when any of the consumers of the GDSCs (in this case USB)
> votes on a perforamance state, genpd framework can identify that
> the GDSC itself does not support a performance state and it
> then propogates the vote to the parent, which in this case is cx.
> 
> This change would also mean that any GDSC in GCC thats left enabled
> during low power state (perhaps because its marked with a
> ALWAYS_ON flag) can prevent the system from entering low power
> since that would prevent cx from transitioning to low power.
> Ideally any consumers that would need to have their devices
> (partially) powered to support wakeups should look at making the
> resp. GDSCs transtion to a Retention (PWRSTS_RET) state instead
> of leaving them ALWAYS_ON.
> 
> Signed-off-by: Rajendra Nayak <quic_rjendra@...cinc.com>

I suppose a similar patch is needed for sc7180?