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Date:   Tue, 13 Sep 2022 11:30:36 +0200
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Subject: Re: [PATCH v2 06/13] dt-bindings: serial: atmel,at91-usart: Add
 SAM9260 compatibles to SAM9x60
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To:     Sergiu.Moga@microchip.com, robh@kernel.org
Cc:     lee@kernel.org, krzysztof.kozlowski+dt@linaro.org,
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From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <888b8ab9-f8cb-2e1f-465c-3cb97187fce0@microchip.com>
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On 13/09/2022 11:19, Sergiu.Moga@microchip.com wrote:
>>
>> Let me rephrase it:
>>
>> What your commit is doing is requiring additional fallback compatibles.
>> Therefore the commit msg should answer - why do you require additional
>> fallback compatibles?
>>
> 
> 
> The additional fallback compatibles are required because the driver in 
> question only knows about the atmel,at91sam9260-usart compatible. 
> Furthermore, it is also a better representation of the fact that the 
> serial IP of 9x60 is an improvement over the serial IP of 9260 (it 
> contains more hardware features not yet implemented in the driver).
> 
> 
>> Incremental characteristics sound to me optional. I can increment
>> sam9x60 with something or I can skip it. But you are not doing it...
>> sam9x60 was already there and now you require a fallback.
>>
>> Best regards,
>> Krzysztof
> 
> So, what is your opinion on the following commit message:
> 
> "Fix sam9x60 compatible list by adding the sam9260 compatibles as 
> fallback, since the atmel_serial driver only knows of the latter's 
> compatible. The atmel_serial driver only has knowledge of the sam9260 
> compatible because it does not have the sam9x60's serial IP specific 
> features implemented yet and adding an empty compatible without adding 
> support specific to that compatible would be misleading. Thus prefer the 
> fallback mechanism in the detriment of adding an empty compatible in the 
> driver."

It's fine. Also could work:

"Require sam9260 fallback compatible for sam9x60, because sam9x60 is
fully compatible with sam9260 and Linux driver requires the latter."

If it fixes any observable issue like lack of driver binding to DTS, you
can also mention that.

Best regards,
Krzysztof