Re: [PATCH 2/8] dt-bindings: soc: qcom: eud: Add usb role switch property

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 1.08.2024 9:46 AM, Krzysztof Kozlowski wrote:
> On 01/08/2024 02:16, Elson Serrao wrote:
>>
>>
>> On 7/30/2024 10:36 PM, Krzysztof Kozlowski wrote:
>>> On 31/07/2024 00:24, Elson Roy Serrao wrote:
>>>> EUD hub is physically present in between the USB connector and the
>>>> USB controller. So the role switch notifications originating from
>>>> the connector should route through EUD. Hence to interpret the usb
>>>> role assigned by the connector, role switch property is needed.
>>>>
>>>> Signed-off-by: Elson Roy Serrao <quic_eserrao@quicinc.com>
>>>> ---
>>>>  Documentation/devicetree/bindings/soc/qcom/qcom,eud.yaml | 4 ++++
>>>>  1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/soc/qcom/qcom,eud.yaml b/Documentation/devicetree/bindings/soc/qcom/qcom,eud.yaml
>>>> index fca5b608ec63..0fa4608568d0 100644
>>>> --- a/Documentation/devicetree/bindings/soc/qcom/qcom,eud.yaml
>>>> +++ b/Documentation/devicetree/bindings/soc/qcom/qcom,eud.yaml
>>>> @@ -37,6 +37,10 @@ properties:
>>>>      items:
>>>>        - const: usb2-phy
>>>>  
>>>> +  usb-role-switch:
>>>> +    $ref: /schemas/types.yaml#/definitions/flag
>>>> +    description: Support role switch.
>>>
>>> So both EUD and DWC3 controller (as this binding states) are role switching?
>>>
>>
>> Yes. EUD would receive roles from the connector and relay it to the DWC3 controller. In addition to these roles, the DWC3 controller
>> would also receive roles from EUD itself (related to USB attach/detach events).
> 
> Does not look right. Seems like you add something because it is easier
> to code in drivers.

Perhaps that's semantics.. EUD can be thought of as something approximating
USB-C (very loosely). If you program it right, it exposes a USB hub full of
"""altmodes""" (debug components visible as separate USB peripherals, really)

We need it to know when the device is connected in USB device mode (vs host),
so that we don't accidentally undermine the rest of the USB hardware by
de-muxing the usb controller from a direct connection to the PHY.

Konrad