linux-kernel - Re: [PATCH v2 3/5] dt-bindings: phy: qcom,sc8280xp-qmp-usb43dp-phy: Document static lanes mapping

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Message-ID: <418ba924-7e3d-474f-ab1e-084ca8ad313d@linaro.org>
Date: Wed, 3 Sep 2025 09:49:51 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, dri-devel@...ts.freedesktop.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org
Subject: Re: [PATCH v2 3/5] dt-bindings: phy: qcom,sc8280xp-qmp-usb43dp-phy:
 Document static lanes mapping

On 03/09/2025 09:07, Krzysztof Kozlowski wrote:
> On Tue, Sep 02, 2025 at 11:00:30AM +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
>>
>> The layout of the lanes was designed to be mapped and swapped
>> related to the USB-C Power Delivery negociation, so it supports
>> a finite set of mappings inherited by the USB-C Altmode layouts.
>>
>> Nevertheless those QMP Comby PHY can be statically used to
>> drive a DisplayPort connector, DP->HDMI bridge, USB3 A Connector,
>> etc... without an USB-C connector and no PD events.
> 
> What is the use case for static mapping? Embedded HDMI port on T14s
> laptop?
> 
>>
>> Add a property that documents the static lanes mapping to
>> each underlying PHY to allow supporting boards directly
>> connecting USB3 and DisplayPort lanes to the QMP Combo
>> lanes.
>>
>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>> ---
>>   .../phy/qcom,sc8280xp-qmp-usb43dp-phy.yaml         | 29 ++++++++++++++++++++++
>>   1 file changed, 29 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..12511a462bc6245e0b82726d053d8605148c5047 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 +76,35 @@ properties:
>>     mode-switch: true
>>     orientation-switch: true
>>   
>> +  qcom,static-lanes-mapping:
>> +    $ref: /schemas/types.yaml#/definitions/uint32-array
>> +    minItems: 4
>> +    items:
>> +      enum:
>> +        - 0 # Unconnected (PHY_NONE)
>> +        - 4 # USB3 (PHY_TYPE_USB3)
>> +        - 6 # DisplayPort (PHY_TYPE_DP)
>> +    description:
>> +      Describes the static mapping of the Combo PHY lanes, when not used
>> +      a in a Type-C dynamic setup using USB-C PD Events to change the mapping.
>> +      The 4 lanes can either routed to the underlying DP PHY or the USB3 PHY.
>> +      Only 2 of the lanes can be connected to the USB3 PHY, but the 4 lanes can
>> +      be connected to the DP PHY.
>> +      The numbers corresponds to the PHY Type the lanes are connected to.
>> +      The possible combinations are
>> +        <0 0 0 0> when none are connected
>> +        <4 4 0 6> USB3 and DP single lane
>> +        <4 4 6 6> USB3 and DP
>> +        <6 6 4 4> DP and USB3
>> +        <6 0 4 4> DP and USB3 single lane
> 
>> +        <4 4 0 0> USB3 Only
>> +        <0 0 4 4> USB3 Only
> 
> Why do you need to handle here and in few other places mirrored case?
> Isn't enough to just say you only want USB3? Maybe my first question
> (what is usecase for this) answers this, though.

Usecase is larger than the HDMI on the T14s, we must handle boards directly
connected some USB-A and DP stuff directly on the combo lanes.

See https://lore.kernel.org/all/8A7C126C22789C9B+f30def47-302a-45ee-8f76-64ef277f773f@radxa.com/

> 
> This looks similar to rockchip,dp-lane-mux, from the objective point of
> view. Please look there and if it is really similar concept this would
> warrant having it as generic property in video-interfaces for example.

Yes it's quite the same

> 
> I also wonder if this should not be stored in the endpoint.

But I'm trying to store this in the endpoint as [1], the Bindings & DT part looks fine,
but the driver part looks horrible...

I'll probably post an RFC of that shortly

[1] https://lore.kernel.org/all/14f334fc-35de-4f21-8eb1-f6b41ac24704@linaro.org/

Neil

> 
> Best regards,
> Krzysztof
>