RE: [PATCH v8 1/2] dt-bindings: usb: cdns3: Add cdns,cdnsp-no-drd compatible string

[Pawel Laszczak]

>
>On Fri, May 15, 2026 at 01:24:38PM +0200, Pawel Laszczak via B4 Relay wrote:
>> From: Pawel Laszczak <pawell@xxxxxxxxxxx>
>>
>> Introduce a new compatible string 'cdns,cdnsp-no-drd' for Cadence
>> USBSS/USBSSP controllers to support hardware configurations where the
>> Dual-Role Device (DRD) register block is missing or inaccessible.
>>
>> This change follows the recommendation to imply hardware limitations
>> directly from the compatible string rather than using a dedicated
>> boolean property.
>>
>> When 'cdns,cdnsp-no-drd' is used:
>> - The 'otg' register and interrupt resources are not required.
>> - The 'reg' and 'interrupts' properties are restricted to 2 items
>>   (host and device).
>> - 'dr_mode' must be explicitly set to either 'host' or 'peripheral'.
>>
>> The standard 'cdns,usb3' compatible remains unchanged, maintaining
>> backward compatibility by requiring all 3 resource sets (otg, host, dev).
>>
>> Signed-off-by: Pawel Laszczak <pawell@xxxxxxxxxxx>
>> ---
>> v8:
>> - Update commit message to reflect schema changes.
>> - Removed 'cdns,no-drd' boolean property as per Rob Herring's suggestion.
>> - Introduced a new compatible string 'cdns,cdnsp-no-drd' for controller
>>   variants that lack the DRD/OTG register block.
>>
>> v7:
>> - Rename 'no_drd' to 'cdns,no-drd'.
>> - Update commit message to reflect property renaming and schema
>changes.
>> - Simplify 'reg-names' using a single enum.
>> - Revert 'interrupt-names' to a list of constants.
>> - Move 'reg' item descriptions to if/else blocks for accuracy.
>> - Clean up 'if/then' logic (remove redundant checks).
>> - Add explicit 'items' list for 'interrupt-names' in the 'else' block.
>>
>> v6:
>> - Fixed validation error for 'interrupt-names' by correcting
>>   the items definition.
>> - Adjusted 'minItems'/'maxItems' to properly support the optional
>>  'wakeup' interrupt.
>> - Fixed 'too long' schema error in examples.
>>
>> v5:
>> - Implemented strict conditional validation using if-then-else logic.
>> - Enforced 2 register/interrupt items and required 'dr_mode'
>>   (host or peripheral) when 'no_drd' is present.
>> - Enforced the standard 3 register/interrupt items (otg, host, dev)
>>   when 'no_drd' is absent to ensure backward compatibility.
>> - Updated 'reg-names' and 'interrupt-names' to use enums in the main
>>   properties section to support flexible resource ordering during
>>   validation.
>> ---
>> ---
>>  .../devicetree/bindings/usb/cdns,usb3.yaml         | 60
>++++++++++++++++++----
>>  1 file changed, 50 insertions(+), 10 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/usb/cdns,usb3.yaml
>b/Documentation/devicetree/bindings/usb/cdns,usb3.yaml
>> index 2d95fb7321af..7b0aa9c4a2bd 100644
>> --- a/Documentation/devicetree/bindings/usb/cdns,usb3.yaml
>> +++ b/Documentation/devicetree/bindings/usb/cdns,usb3.yaml
>> @@ -17,22 +17,22 @@ description:
>>
>>  properties:
>>    compatible:
>> -    const: cdns,usb3
>> +    enum:
>> +      - cdns,usb3
>> +      - cdns,cdnsp-no-drd
>
>I doubt this is what Rob meant, he asked for soc-specific compatibles
>and this is generic. A soc-specific compatible would be something like
>microchip,newsoc-usb3

Hi Conor, Rob

To clarify the hardware situation: I am developing and testing this on
an FPGA development board connected via pure PCI, without any Device Tree.
I do not have a specific SoC platform, nor do I know what silicon target
the end customers will use in the future.
Introducing a fake SoC-specific compatible string just to pass the DT
validation feels misleading and unnecessary.

Since cdns,usb3 is already an established generic compatible, and we
cannot use a generic configuration string like cdns,cdnsp-no-drd,
the cleanest way forward is to make this resource-driven instead of
compatible-driven.

In v9, I propose to:
 - Keep only the existing cdns,usb3 compatible.
 - Update cdns,usb3.yaml to allow minItems: 2 for reg and reg-names
   if dr_mode is explicitly set to "host" or "peripheral" (indicating
   that the OTG register block is absent).
 - In the driver code, determine the lack of DRD dynamically if the "otg"
   resource/register block is missing.

This elegantly solves the issue for my PCI/FPGA platform (where I just
won't pass the "otg" resource), complies with DT practices, and leaves
the door open for any future customer SoC to use cdns,usb3 with
standard dr_mode constraints.

Does this approach look acceptable to you?

Thanks,
Pawel

>
>Thanks,
>Conor.
>
>>
>>    reg:
>> -    items:
>> -      - description: OTG controller registers
>> -      - description: XHCI Host controller registers
>> -      - description: DEVICE controller registers
>> +    minItems: 2
>> +    maxItems: 3
>>
>>    reg-names:
>> +    minItems: 2
>> +    maxItems: 3
>>      items:
>> -      - const: otg
>> -      - const: xhci
>> -      - const: dev
>> +      enum: [ otg, xhci, dev ]
>>
>>    interrupts:
>> -    minItems: 3
>> +    minItems: 2
>>      items:
>>        - description: XHCI host controller interrupt
>>        - description: Device controller interrupt
>> @@ -41,7 +41,7 @@ properties:
>>                       cleared by xhci core, this interrupt is optional
>>
>>    interrupt-names:
>> -    minItems: 3
>> +    minItems: 2
>>      items:
>>        - const: host
>>        - const: peripheral
>> @@ -93,6 +93,46 @@ allOf:
>>    - $ref: usb-drd.yaml#
>>    - $ref: usb-xhci.yaml#
>>
>> +  - if:
>> +      properties:
>> +        compatible:
>> +          const: cdns,cdnsp-no-drd
>> +    then:
>> +      properties:
>> +        reg:
>> +          items:
>> +            - description: XHCI Host controller registers
>> +            - description: DEVICE controller registers
>> +        reg-names:
>> +          items:
>> +            - const: xhci
>> +            - const: dev
>> +        interrupts:
>> +          maxItems: 2
>> +        interrupt-names:
>> +          items:
>> +            - const: host
>> +            - const: peripheral
>> +        dr_mode:
>> +          enum: [host, peripheral]
>> +    else:
>> +      properties:
>> +        reg:
>> +          items:
>> +            - description: OTG controller registers
>> +            - description: XHCI Host controller registers
>> +            - description: DEVICE controller registers
>> +        reg-names:
>> +          items:
>> +            - const: otg
>> +            - const: xhci
>> +            - const: dev
>> +        interrupts:
>> +          minItems: 3
>> +          maxItems: 4
>> +        interrupt-names:
>> +          minItems: 3
>> +
>>  unevaluatedProperties: false
>>
>>  examples:
>>
>> --
>> 2.43.0
>>
>>