linux-kernel - Re: [PATCH RFC 1/3] dt-bindings: phy: qcom,sc8280xp-qmp-usb43dp-phy: Document default phy mode

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Message-ID: <yc7ceoq3bn3lkxdwkrk64ecubej64vblpwlwzyj5cuep2wmjui@nln2t2yicu7o>
Date: Fri, 22 Aug 2025 13:57:07 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-phy@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/3] dt-bindings: phy: qcom,sc8280xp-qmp-usb43dp-phy:
 Document default phy mode

On Thu, Aug 21, 2025 at 03:53:26PM +0200, Neil Armstrong wrote:
> The QMP USB3/DP Combo PHY hosts an USB3 phy and a DP PHY on top
> of a combo glue to route either lanes to the 4 shared physical lanes.
> 
> The routing of the lanes can be:
> - 2 DP + 2 USB3
> - 4 DP
> - 2 USB3
> 
> And the layout of the lanes can be swpped depending of an
> eventual USB-C connector orientation.
> 
> Nevertheless those QMP Comby PHY can be statically used to
> drive a DisplayPort connector, DP->HDMI bridge, USB3 A Connector...
> 
> But if a 4lanes DP->HDMI bridge is directly connected to the
> QMP Comby PHY lanes, in the default routing 2 or the 4 lanes would
> probbaly be USB3, making the DP->HDMI bridge non functional.
> 
> Add a property to hint in which layout mode the QMP Comby PHY
> should be as startup.
> 
> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> ---
>  .../bindings/phy/qcom,sc8280xp-qmp-usb43dp-phy.yaml         | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-usb43dp-phy.yaml b/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-usb43dp-phy.yaml
> index c8bc512df08b5694c8599f475de78679a4438449..129475a1d9527733e43ded5a38aad766f9810fe7 100644
> --- a/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-usb43dp-phy.yaml
> +++ b/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-usb43dp-phy.yaml
> @@ -76,6 +76,19 @@ properties:
>    mode-switch: true
>    orientation-switch: true
>  
> +  qcom,combo-initial-mode:
> +    description:
> +      Describe the initial mode of the Combo PHY configuration.
> +      The Combo PHY is a wrapper on top of a DP PHY and an USB3 PHY,
> +      sharing the same SuperSpeed lanes with either DisplayPort over
> +      the 4 lanes (dp), USB3 on a pair of lanes (usb3) or both
> +      technologies in a 2+2 configuration (usb3+dp) as default.

SPecifying this as an initial mode means that it can be switched later.
Should we generalize this and desribe it as bus-type (from
video-interfaces.yaml) and allow it to be present only if there is no
mode-switch property?


> +    default: usb3+dp
> +    enum:
> +      - usb3+dp
> +      - usb3
> +      - dp
> +
>    ports:
>      $ref: /schemas/graph.yaml#/properties/ports
>      properties:
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry