Re: [PATCH v2 1/1] dt-bindings: connector: Add role‑switch provider phandle

[Elson Serrao]

On 3/25/2026 6:57 PM, Dmitry Baryshkov wrote:
> On Thu, 26 Mar 2026 at 03:49, Elson Serrao
> <elson.serrao@xxxxxxxxxxxxxxxx> wrote:
>>

[...]

>>>
>>> Previously we didn't have such an issue for the usb-role-switch,
>>> because there always have been a direct link between the USB connector
>>> (be it gpio-usb-b-connector or usb-c-connector) and the USB controller
>>> (implementing usb-role-switch). As with the EUD this is no longer a
>>> case, my suggestion would be to follow prior art and let EUD receive,
>>> interpret and resend usb-role-switch events.
>>>
>>
>> In this topology, the EUD hardware spans more than one independent
>> role-switch relationship, as a single EUD node is the direct neighbor of
>> multiple connectors. This introduces additional considerations around
>> role-switch discovery.
>>
>> One practical consideration if the EUD registers multiple role-switch
>> instances is that fwnode_usb_role_switch_get() ( which relies on
>> class_find_device_by_fwnode API), assumes a unique firmware node per
>> role-switch instance. If multiple role-switch instances are registered
>> against the same firmware node (the EUD fwnode), the lookup will return
>> only the first registered instance, making it difficult for a connector to
>> reliably bind to its intended role-switch provider.
>>
>> Supporting multiple role-switch instances in this model would therefore
>> require extending the lookup mechanism to allow additional disambiguation
>> (for example, associating role-switch instances with connector context).
>>
>> I want to make sure I clearly understand the intended modeling and whether
>> these USB role-switch framework implications are considered acceptable.
> 
> As far as I can see, you can register two usb-role-switches, one per
> the EUD path. then the connector will still be able to discover
> correct switch by following the chain from the connector. On the other
> hand, the EUD driver can use fwnode_usb_role_switch_get() passing the
> path's fwnode and find the next role-switch connected to the each of
> the EUD ports / paths.
> 

My earlier questions were primarily around a flattened ports representation.
I agree that modeling each EUD path as a distinct child node with its own
firmware node addresses those concerns cleanly.

For context, the existing EUD binding [1] models a single controller ↔
connector relationship using a flat top-level ports block. An earlier
attempt [2] to reinterpret that top-level structure to represent
multiple paths ran into DT ABI concerns, as it changed the meaning of
existing bindings.

Based on your example, my understanding is that the intended direction is
to keep the existing top-level `ports` semantics unchanged for backward
compatibility, and model multi-path hardware using explicit child nodes,
each representing one controller ↔ connector relationship and registering
a separate usb-role-switch instance.

Please let me know if this matches the intended direction.

For the purposes of the usb‑role‑switch discussion, the other feedback in
[2] around PHY handling is orthogonal and will be addressed in a follow‑up
revision.

Thanks,
Elson

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/devicetree/bindings/soc/qcom/qcom,eud.yaml?h=v7.0-rc5
[2] https://lore.kernel.org/all/20260126233830.2193816-2-elson.serrao@xxxxxxxxxxxxxxxx/

> Here I am assuming that EUD device structured in a way like:
> 
> eud {
>   compatible = "qcom,eud";
> 
>   path@0 {
>     ports {
>       port@0 {
>         endpoint {
>           remote-endpoint = <&usb_con_0_hs>;
>         };
>       };
>       port@1 {
>         endpoint {
>           remote-endpoint = <&usb0_hs>;
>         };
>       };
>     };
>   };
> 
>   path@1 {
>     ports {
>       port@0 {
>         endpoint {
>           remote-endpoint = <&usb_con_1_hs>;
>         };
>       };
>       port@1 {
>         endpoint {
>           remote-endpoint = <&usb1_hs>;
>         };
>       };
>     };
>   };
> 
> };
>