linux-kernel - Re: [PATCH v2 1/9] dt-bindings: soc: qcom: eud: Restructure to model multi-path hardware

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Message-ID: <a61eab24-a5d9-4253-b27d-89961b62665d@oss.qualcomm.com>
Date: Tue, 3 Feb 2026 14:35:30 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Elson Serrao <elson.serrao@....qualcomm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Souradeep Chowdhury <quic_schowdhu@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/9] dt-bindings: soc: qcom: eud: Restructure to model
 multi-path hardware

On 1/27/26 12:38 AM, Elson Serrao wrote:
> The Qualcomm Embedded USB Debugger (EUD) can intercept one or two
> independent High-Speed UTMI paths, depending on the SoC. Each path is
> distinct with its own HS-PHY interface, connector/controller wiring, and
> UTMI routing behavior. The EUD hardware sits between the USB2 PHY and
> the USB controller on each path.
> 
> The existing binding models only a single UTMI path and does not provide
> a way to associate the required High-Speed USB PHY. EUD relies on the
> HS-PHY on the selected UTMI path for link signalling and correct operation
> of the hardware.
> 
> Historically, EUD has worked on platforms that use a single UTMI path
> because the USB controller maintains ownership of the PHY during
> enumeration and normal operation. This implicit relationship allowed
> EUD to function even though the dependency on the PHY was not described
> in the binding. However, this behavior is not guaranteed by hardware.
> The current binding description is not sufficient for SoCs that expose
> two independent UTMI paths, where the PHY association and port wiring
> must be explicitly described.
> 
> Introduce per-path eud-path child nodes so each UTMI path can describe
> its HS-PHY, port connections, and the role‑switching capability of its
> associated USB port.
> 
> Signed-off-by: Elson Serrao <elson.serrao@....qualcomm.com>
> ---

[...]

> +patternProperties:
> +  "^eud-path@[0-1]$":

I can't quite put it into words why I don't like this name, but I
don't like this name.. That said I don't really have any clever ideas
for a better one, so I'm not going to object, suppose I just needed
to vent my ramblings

> +    type: object
>      description:
> -      These ports is to be attached to the endpoint of the DWC3 controller node
> -      and type C connector node. The controller has the "usb-role-switch"
> -      property.
> +      Represents one High-Speed UTMI path that EUD intercepts. This node models
> +      the physical data path intercepted by EUD and provides graph endpoints to
> +      link the USB controller and the external connector associated with this path.
>  
>      properties:
> -      port@0:
> -        $ref: /schemas/graph.yaml#/properties/port
> -        description: This port is to be attached to the DWC3 controller.
> +      reg:
> +        maxItems: 1
> +        description: Path number
> +
> +      phys:
> +        maxItems: 1
> +        description: High-Speed USB PHY associated with this data path.
> +
> +      usb-role-switch:
> +        type: boolean
> +        description:
> +          Set this property if the USB port on this path is role switch capable.

This doesn't quite sound right. The EUD acts/can act as a rolesw no matter
what's connected to it.

> +          In device role, debug mode inserts the EUD hub into the UTMI path. In
> +          host role, the EUD hub is bypassed and UTMI traffic flows directly
> +          between the PHY and the USB controller.

The rest of this paragraph is good stuff, explaining the reasoning

> +
> +      ports:
> +        $ref: /schemas/graph.yaml#/properties/ports
> +        description:
> +          These ports are to be attached to the endpoint of the USB controller node
> +          and USB connector node.
> +
> +        properties:
> +          port@0:
> +            $ref: /schemas/graph.yaml#/properties/port
> +            description: This port is to be attached to the USB controller.
>  
> -      port@1:
> -        $ref: /schemas/graph.yaml#/properties/port
> -        description: This port is to be attached to the type C connector.

nit: "Type-C"

Konrad