Re: [PATCH v2 1/6] dt-bindings: media: renesas,isp: Add Gen4 family fallback

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On 27/08/2024 23:34, Laurent Pinchart wrote:
> On Tue, Aug 27, 2024 at 10:12:33AM +0200, Niklas Söderlund wrote:
>> On 2024-08-27 08:31:22 +0200, Krzysztof Kozlowski wrote:
>>> On Mon, Aug 26, 2024 at 04:43:47PM +0200, Niklas Söderlund wrote:
>>>> The ISP Channel Selector IP is the same for all current Gen4 devices.
>>>> This was not known when adding support for V3U and V4H and a single SoC
>>>> specific compatible was used.
>>>>
>>>> Before adding more SoC specific bindings for V4M add a family compatible
>>>> fallback for Gen4. That way the driver only needs to be updated once for
>>>> Gen4, and we still have the option to fix any problems in the driver if
>>>> any testable differences between the SoCs are found.
>>>>
>>>> There are already DTS files using the V3U and V4H compatibles which
>>>> needs to be updated to not produce a warning for DTS checks. The driver
>>>> also needs to kept the compatible values to be backward compatible , but
>>>> for new Gen4 SoCs such as V4M we can avoid this.
>>>>
>>>> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
>>>> ---
>>>> * Changes since v1
>>>> - New in v2.
>>>> ---
>>>>  Documentation/devicetree/bindings/media/renesas,isp.yaml | 3 ++-
>>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/media/renesas,isp.yaml b/Documentation/devicetree/bindings/media/renesas,isp.yaml
>>>> index 33650a1ea034..730c86f2d7b1 100644
>>>> --- a/Documentation/devicetree/bindings/media/renesas,isp.yaml
>>>> +++ b/Documentation/devicetree/bindings/media/renesas,isp.yaml
>>>> @@ -22,6 +22,7 @@ properties:
>>>>        - enum:
>>>>            - renesas,r8a779a0-isp # V3U
>>>>            - renesas,r8a779g0-isp # V4H
>>>> +      - const: renesas,rcar-gen4-isp # Generic R-Car Gen4
>>>
>>> Adding generic fallback post-factum is odd, does not feel reliable.
>>> Instead use specific compatibles as fallbacks.
>>
>> I agree, it feels a bit odd. But this was the road we hammered out at 
>> great pain for how to be able to move forward with this issue for the 
>> other IP block involved in video capture for R-Car Gen4, VIN [1]. This 
>> just mirrors that long discussion decision for the R-Car CSISP.
>>
>> I would hate to have different solutions for the two.
>>
>> 1. [PATCH v5 0/6] rcar-vin: Add support for R-Car V4M
>>    https://lore.kernel.org/all/20240704161620.1425409-1-niklas.soderlund+renesas@xxxxxxxxxxxx/
> 
> The compatible fallback for VIN has been added following a request from
> Conor and Rob, so it would be nice if the three of you could agree to
> achieve consistency in the bindings :-)

Don't twist our answers. You need fallback, but specific, not family.
There was a countless number of answers from Rob that specific
compatibles are preferred.

Look, Conor's reply:

https://lore.kernel.org/all/20240620-gating-coherent-af984389b2d7@spud/
Do you see family fallback? I think "r8a779g0" is SoC.

Look here:
https://lore.kernel.org/all/20240610-screen-wolverine-78370c66d40f@spud/

Or here
https://lore.kernel.org/all/20240624-rented-danger-300652ab8eeb@wendy/
where Conor agrees against!

So let me actually NAK it - you got multiple comments on VIN to use
specific compatible.

Best regards,
Krzysztof





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