Re: [PATCH v1 1/4] dt-bindings: iio: adc: amlogic,meson-saradc: add S4 compatible

From: Krzysztof Kozlowski <krzk@kernel.org>
To: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Nick Xie <nick@khadas.com>,
	neil.armstrong@linaro.org, khilman@baylibre.com,
	jbrunet@baylibre.com, krzk+dt@kernel.org, jic23@kernel.org,
	dlechner@baylibre.com, nuno.sa@analog.com, andy@kernel.org,
	linux-iio@vger.kernel.org, robh@kernel.org, conor+dt@kernel.org,
	linux-amlogic@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, xieqinick@gmail.com
Subject: Re: [PATCH v1 1/4] dt-bindings: iio: adc: amlogic,meson-saradc: add S4 compatible
Date: Mon, 2 Mar 2026 14:59:21 +0100	[thread overview]
Message-ID: <49b3a87d-7ea0-4da1-871e-35ddf5d5b454@kernel.org> (raw)
In-Reply-To: <CAFBinCAkxO4HoN0Cw0Fc2B3KRLLJqso1p5+qjNN_E0c26VOf2g@mail.gmail.com>

On 02/03/2026 12:58, Martin Blumenstingl wrote:
> Hi Krzysztof,
> 
> On Sat, Feb 28, 2026 at 12:18 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>>
>> On Sat, Feb 28, 2026 at 02:58:37PM +0800, Nick Xie wrote:
>>> Add the compatible string for the SARADC (Successive Approximation
>>> Register ADC) IP block found in the Amlogic Meson S4 SoC.
>>
>> ... which is fully compatible with g12a?
>>
>> Write proper explanations.
> Would you be fine with:
> "There are no known differences between the SARADC on S4 and the one
> on G12A. In the past differences between SARADC on the different SoCs
> generations have been uncovered late, meaning that a dedicated
> compatible string has proven to be useful."

No, last sentence is redundant. You do not need to explain in the commit
msg rules of bindings, because they are obvious/known. You need to
explain the hardware, e.g. in this case the compatibility between devices.

> 
> Do you also require Nick to add amlogic,meson-g12a-saradc as fallback
> compatible string for amlogic,meson-s4-saradc?
> 
>>>
>>> Signed-off-by: Nick Xie <nick@khadas.com>
>>> ---
>>>  .../devicetree/bindings/iio/adc/amlogic,meson-saradc.yaml        | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/iio/adc/amlogic,meson-saradc.yaml b/Documentation/devicetree/bindings/iio/adc/amlogic,meson-saradc.yaml
>>> index bb9825e7346dd..5496a0dc714aa 100644
>>> --- a/Documentation/devicetree/bindings/iio/adc/amlogic,meson-saradc.yaml
>>> +++ b/Documentation/devicetree/bindings/iio/adc/amlogic,meson-saradc.yaml
>>> @@ -27,6 +27,7 @@ properties:
>>>                - amlogic,meson-gxm-saradc
>>>                - amlogic,meson-axg-saradc
>>>                - amlogic,meson-g12a-saradc
>>> +              - amlogic,meson-s4-saradc
>>
>> If this is compatible with other device, you need proper fallback.
>>
>>>            - const: amlogic,meson-saradc
>>
>> And this one is now kind of fake - how does this device use it?
> As you have noticed later, it is currently not used.
> Can you please confirm that my understanding of the next steps is correct:
> - you're expecting Nick to omit the amlogic,meson-saradc fallback
> compatible string for amlogic,meson-s4-saradc

Not omit but replace with proper fallback to specific compatible.

> - and you would like to see amlogic,meson-saradc removed (from the
> bindings and .dts files that are already upstream) - I will take care
> of this once S4 support lands upstream

This no. It's an ABI, you cannot change it. Not worth it, either.

Best regards,
Krzysztof

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