Re: [PATCH v9 4/8] usb: misc: qcom_eud: add per-path role switch support

[Konrad Dybcio]

On 10/17/26 3:16 AM, Elson Serrao wrote:
> 
> 
> On 10/15/2026 7:43 AM, Konrad Dybcio wrote:
>> On 9/29/26 11:35 PM, Elson Serrao wrote:
>>> The EUD hardware can support multiple High-Speed USB paths, each connected
>>> to different USB controllers. The current implementation uses a single
>>> chip-level role switch, which cannot properly handle multi-path
>>> configurations where each path needs independent role management. Since
>>> EUD is physically present between the USB connector and the controller,
>>> it should also relay the role change requests from the connector.
>>>
>>> Restructure the driver to support per-path role switches and remove the
>>> chip-level role switch. Additionally, as EUD need not modify the USB
>>> role upon enabling, remove the unnecessary role switch call from
>>> enable_eud().
>>>
>>> Reviewed-by: Peter Chen <peter.chen@xxxxxxxxxx>
>>> Signed-off-by: Elson Serrao <elson.serrao@xxxxxxxxxxxxxxxx>
>>> ---
>>
>>
>> [...]
>>
>>> +	sw = usb_role_switch_find_by_fwnode(of_fwnode_handle(controller_node));
>>> +	if (!sw) {
>>> +		of_node_put(controller_node);
>>> +		return dev_err_probe(chip->dev, -EPROBE_DEFER,
>>> +				     "Failed to get controller role switch for path %d\n",
>>> +				     path_num);
>>> +	}
>>
>> This will always probe defer on a fixed-role controller, we should patch
>> dwc3 to always register a roleswitch
>>
> You mean for fixed-role controllers where an explicit `dr_mode` is not
> provided in DT and the fixed mode is derived from the HW capabilities?
> For explicit `dr_mode=host/peripheral` cases we bail out earlier and
> never reach this path.
> 
> The EUD databook does not explicitly mention fixed-role controllers,
> so I was assuming all DWC3 controllers relevant to EUD are DR-capable
> and register a role switch.
> 
> I can see how a no-op role switch would address this case. Would it be
> reasonable to handle that as a follow-up improvement for controllers
> that resolve to a fixed role at runtime, rather than as part of this
> series?

I think so. Generally true-non-dual-role controllers (i.e. by HW
limitation, not through DT/firmware configuration) are probably
unlikely to ever be hooked up to EUD.

Konrad