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: <kxevo35c7tsbjeu4b7ep3f4eld5t4ohy35x4igaki6n7uvteev@ifotwczstsn3>
Date: Fri, 22 Aug 2025 14:39:47 +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 Fri, Aug 22, 2025 at 01:02:21PM +0200, Neil Armstrong wrote:
> On 22/08/2025 12:57, Dmitry Baryshkov wrote:
> > 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?
> 
> I was not sure about that, and yes we should do that instead but I'm not
> sure about how.
> 
> bus-type sounds great, but the numbering doesn't match so I was thinking instead
> something like phy-type with a string or use the numbers from include/dt-bindings/phy/phy.h

Well... we can add more entries there and map them in the driver.

> 
> The thing is, do we want to keep the dual dp+usb3 as static ? I think it's very possible
> a board would connect the combo phy to an USB3 A connector and a 2lanes DisplayPort connector.

I'm not sure I follow the question. Could you please explain what you've
meant here?


-- 
With best wishes
Dmitry