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

[Neil Armstrong <neil.armstrong@linaro.org>]

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@linaro.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

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.

Neil

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