Re: [PATCH 2/2] dt-bindings: usb: cdns,usb3: Add support for USBSSP

[Krzysztof Kozlowski <krzk@kernel.org>]

On 02/03/2026 10:21, Peter Chen wrote:
> On 26-03-02 08:28:07, Krzysztof Kozlowski wrote:
>>
>> On Mon, Mar 02, 2026 at 11:03:34AM +0800, Peter Chen wrote:
>>> Extend the Cadence USBSS DRD binding to also cover the USBSSP
>>> controller by adding "cdns,usbssp" to the compatible enum.
>>>
>>> The USBSSP is the next-generation Cadence USB controller IP. It adds
>>> SuperSpeed Plus (USB 3.1 gen2x1, 10 Gbps) support and uses an
>>> XHCI-based device controller. The register layout and resource model
>>> (otg/xhci/dev memory regions; host/peripheral/otg interrupts) are
>>> identical to the USBSS, so both controllers share the same binding
>>> and the same platform driver (cdns3-plat.c).
>>>
>>> Changes to the binding:
>>> - compatible: const -> enum with cdns,usb3 and cdns,usbssp
>>> - maximum-speed: add super-speed-plus
>>> - Add USBSSP example
>>>
>>> This patch was developed with assistance from Anthropic Claude Opus 4.6.
>>
>> Use proper tag, but expect pushback of microslop crap.
> 
> Krzysztof, thanks for your reply.
> 
> I tried to add Assisted-by or Co-developed-by tag, neither can pass
> checkpatch.pl check, it needs a valid email address. See below:
> 
> ERROR: Unrecognized email address: 'Claude (Anthropic Claude Opus 4.6)'
> #45:
> Assisted-by: Claude (Anthropic Claude Opus 4.6)
> 
>>
>>>
>>> Signed-off-by: Peter Chen <peter.chen@cixtech.com>
>>> ---
>>>  .../devicetree/bindings/usb/cdns,usb3.yaml    | 36 +++++++++++++++++--
>>>  1 file changed, 33 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/usb/cdns,usb3.yaml b/Documentation/devicetree/bindings/usb/cdns,usb3.yaml
>>> index f454ddd9bbaa..f79333e7fc1f 100644
>>> --- a/Documentation/devicetree/bindings/usb/cdns,usb3.yaml
>>> +++ b/Documentation/devicetree/bindings/usb/cdns,usb3.yaml
>>> @@ -4,14 +4,22 @@
>>>  $id: http://devicetree.org/schemas/usb/cdns,usb3.yaml#
>>>  $schema: http://devicetree.org/meta-schemas/core.yaml#
>>>
>>> -title: Cadence USBSS-DRD controller
>>> +title: Cadence USBSS/USBSSP DRD controller
>>>
>>>  maintainers:
>>>    - Pawel Laszczak <pawell@cadence.com>
>>>
>>> +description:
>>> +  Cadence USB dual-role controllers. USBSS (cdns,usb3) supports up to
>>> +  SuperSpeed (USB 3.0). USBSSP (cdns,usbssp) is the next generation with
>>> +  SuperSpeed Plus (USB 3.1 gen2x1) and XHCI-based device controller. Both
>>> +  share the same register layout and resource model.
>>
>> So are compatible or not?
>>
> 
> Sorry for the misleading description. They are NOT fully compatible.
> The register layout (OTG/XHCI/Device) and interrupts
> (OTG/XHCI/Device/Wakeup) are the same, but register contents are

Layout cannot be the same if contents is different. Same layout means
same register is at the same place. If you have different register with
different contents at given place, how is it "same layout"?

> different, esp, the device (gadget) controllers are architecturally different:
> 
> - USBSS uses a custom gadget controller (cdns3_gadget_init)
> - USBSSP uses an XHCI-based gadget controller (cdnsp_gadget_init)

You just described drivers, so this does not convince me at all.

> 
> I will fix the description in v2 to clearly state this difference.
> 
>>> +
>>>  properties:
>>>    compatible:
>>> -    const: cdns,usb3
>>> +    enum:
>>> +      - cdns,usb3
>>> +      - cdns,usbssp
>>
>> Why do we need another generic compatible?
>>
>> And why do you add it now to each of device schemas using this one?

You did not respond to this one. Look how this schema is used.

> 
> Like explain above, the USBSSP has a different device/gadget controller
> architecture from USBSS. The platform driver uses the compatible string
> to select the correct gadget init function:

Again, driver stuff.

> 
>   if (device_get_match_data(dev) == &cdnsp_plat)
>       cdns->gadget_init = cdnsp_gadget_init;
>   else
>       cdns->gadget_init = cdns3_gadget_init;
> 
> Without a distinct compatible, the driver cannot know which gadget
> controller is present. This is a Cadence IP-level distinction (not
> SoC-specific), so a generic compatible seems appropriate here. But
> please let me know if you'd prefer a different approach.

Generic compatibles are almost never appropriate and driver code rarely
convinces.

Best regards,
Krzysztof