linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: sc8280xp: Correct USB PHY power domains

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Message-ID: <11aa0b82-ddab-4b65-8f49-54e15e0ce44e@linaro.org>
Date: Fri, 29 Dec 2023 16:05:18 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Johan Hovold <johan+linaro@...nel.org>,
 Marijn Suijten <marijn.suijten@...ainline.org>,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Konrad Dybcio <konrad.dybcio@...ainline.org>
Subject: Re: [PATCH 2/3] arm64: dts: qcom: sc8280xp: Correct USB PHY power
 domains

On 29.12.2023 14:25, Johan Hovold wrote:
> [ Please remember to trim your replies and add a newline before your
>   inline comments to make them readable. ]
> 
> On Fri, Dec 29, 2023 at 02:06:26PM +0100, Konrad Dybcio wrote:
>> On 29.12.2023 14:01, Johan Hovold wrote:
>>> On Wed, Dec 27, 2023 at 11:28:27PM +0100, Konrad Dybcio wrote:
> 
>>>> Fix the power-domains assignment to stop potentially toggling the GDSC
>>>> unnecessarily.
>>>
>>> Again, there's no additional toggling being done here, but yes, this may
>>> keep the domains enabled during suspend depending on how the driver is
>>> implemented.
> 
>> No, it can actually happen. (Some) QMP PHYs are referenced by the
>> DP hardware. If USB is disabled (or suspended), the DP being active
>> will hold these GDSCs enabled.
> 
> That's not a "toggling", is it? Also if the DP controller is a consumer of
> these PHY's why should it not prevent the PHYs from suspending?

As far as I'm concerned, "toggling" is the correct word for "switching it
on".. While the PHYs are indeed useful for getting displayport to work,
the USB controller itself may not be necessary there, so enabling its
power line would be a bit of a waste..

Konrad