[RFC PATCH 0/1] dt-bindings: connector: Add role‑switch provider phandle

[Elson Serrao]

Hi all,

This RFC proposes a generic Devicetree mechanism for a USB connector to
reference the USB role‑switch provider when there is an intermediate,
block between the connector and the controller in the OF graph.

Problem
=======
OF‑graph links are strictly point‑to‑point via remote-endpoint, so a
consumer can only discover its immediate neighbor in the graph. When an
intermediate node sits between the USB connector and the controller, the
connector cannot identify the controller (the role‑switch provider) from
the graph alone.

Example (illustrative only)
===========================
On some Qualcomm SoCs, an Embedded USB Debug (EUD) block sits
electrically between USB‑C connectors and DWC3 controllers. EUD models
HS wiring only .

Below is a simplified diagram of the hardware paths:


				EUD Block
			   +------------------------------+  
			   |                              |
[Conn-0]-->[USB2PHY-0]---->|-------- Path 0 --------------|-->[USBCtrl-0]
			   |                              |  
[Conn-1]-->[USB2PHY-1]---->|-------- Path 1 --------------|-->[USBCtrl-1]
			   |                              |
			   |      +------------------+    |
			   |      |  EUD Debug Hub   |    |
			   |      +------------------+    |
			   +------------------------------+

And the corresponding OF‑graph mapping

# Node: EUD (intermediate; graph-only for HS) (extending [1] to dual port)
EUD (eud@...)
└── ports
    ├─ port@0 (reg = <0>)
    │   └─ endpoint  ── remote-endpoint ──>  USBCtrl-0
    │
    ├─ port@1 (reg = <1>)
    │   └─ endpoint  ── remote-endpoint ──>  Conn-0
    │
    ├─ port@2 (reg = <2>)
    │   └─ endpoint  ── remote-endpoint ──>  USBCtrl-1
    │
    └─ port@3 (reg = <3>)
        └─ endpoint  ── remote-endpoint ──>  Conn-1


# Node: Connector 0
Conn-0: usb-connector
└── port
    └─ port@0: endpoint  --> remote-endpoint -->  EUD:port@1

# Node: USB Controller 0
USBCtrl-0: usb@...  (e.g., DWC3-0)
└── port
    └─ port@0: endpoint  --> remote-endpoint -->  EUD:port@0

# Node: Connector 1
Conn-1: usb-connector
└── port
    └─ port@0: endpoint  --> remote-endpoint -->  EUD:port@3

# Node: USB Controller 1
USBCtrl-1: usb@...  (e.g., DWC3)
└── port
    └─ port@0: endpoint  --> remote-endpoint -->  EUD:port@2


>From the OF‑graph structure alone, Conn‑0 cannot determine that
USBCtrl‑0 (and not USBCtrl‑1) is the correct role‑switch provider.

Proposal
========
Add an optional consumer→provider phandle on the connector:

    usb-role-switch = <&controller>;

The provider remains the controller node, which already declares the
boolean 'usb-role-switch;' and registers the role‑switch device.

Request
=======
Please confirm whether adding an optional connector-side provider
phandle is an acceptable general pattern for these topologies. If there
is a more appropriate DT modeling approach for this scenario, I would
appreciate your guidance.

Thanks for your time and review.

Best regards,
Elson Serrao

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/soc/qcom/qcom,eud.yaml?h=v6.19

Elson Serrao (1):
  dt-bindings: connector: Add role‑switch provider phandle

 .../devicetree/bindings/connector/usb-connector.yaml      | 8 ++++++++
 1 file changed, 8 insertions(+)

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2.34.1