linux-kernel - Re: [PATCH] dt-bindings: usb: usb251xb: correct swap-dx-lanes type to uint32

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Date:   Tue, 16 May 2023 10:19:33 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Marek Vasut <marex@...x.de>, mike.looijmans@...ic.nl,
        Richard Leitner <richard.leitner@...ux.dev>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: usb: usb251xb: correct swap-dx-lanes type to
 uint32

On 15/05/2023 15:47, Marek Vasut wrote:
>> Please consider the environment before printing this e-mail
>> On 15-05-2023 14:55, Marek Vasut wrote:
>>> On 5/15/23 12:33, Krzysztof Kozlowski wrote: diff --git 
>>> a/Documentation/devicetree/bindings/usb/usb251xb.yaml 
>>> b/Documentation/devicetree/bindings/usb/usb251xb.yaml
>>>> index 4d1530816817..ac5b99710332 100644
>>>> --- a/Documentation/devicetree/bindings/usb/usb251xb.yaml
>>>> +++ b/Documentation/devicetree/bindings/usb/usb251xb.yaml
>>>> @@ -231,7 +231,7 @@ properties:
>>>>         power-on sequence to a port until the port has adequate power.
>>>>       swap-dx-lanes:
>>>> -    $ref: /schemas/types.yaml#/definitions/uint8-array
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32-array
>>>>       description: |
>>>>         Specifies the ports which will swap the differential-pair 
>>>> (D+/D-),
>>>>         default is not-swapped.
>>>
>>> Would it make more sense to update the driver instead ? I doubt you 
>>> could have more than 256 ports on this device after all.
>>
>>
>> I guess there's a bunch of devicetrees already out there using the 
>> (misdocumented) 32-bit array binding, they'd break in a bad way...
> 
> I think it is the other way around -- if the binding was documented as 
> u8, then the existing DTs should use the u8 type if they are compliant 
> to the binding document.
> 
> I see one board in next which uses this property and sets it to 0 , so 
> this one is not affected either way:
> arch/arm64/boot/dts/freescale/imx8mq-zii-ultra-rmb3.dts: 
> swap-dx-lanes = <0>;


First of all, the original binding did not define it as u8. It actually
skipped the type entirely but:
 - Example shown u32,
 - Driver used u32,
 - In-tree user uses u32 (although as pointed - as 0 so not really
relevant).

Thus the ABI is rather defined by not-breaking users here, so I would
stick to fixing it to u32.

Best regards,
Krzysztof