Re: [PATCH] arm64: dts: qcom: sm8650: add description of CCI controllers

[neil.armstrong@linaro.org]

On 10/04/2024 15:11, Vladimir Zapolskiy wrote:
> On 4/10/24 10:52, Neil Armstrong wrote:
>> Hi,
>>
>> On 10/04/2024 09:49, Vladimir Zapolskiy wrote:
>>> Qualcomm SM8650 SoC has three CCI controllers with two I2C busses
>>> connected to each of them.
>>>
>>> The CCI controllers on SM8650 are compatible with the ones found on
>>> many other older generations of Qualcomm SoCs.
>>>
>>> Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
>>> ---
>>> The change is based and depends on a patch series from Jagadeesh Kona:
>>>
>>>     https://lore.kernel.org/linux-arm-msm/20240321092529.13362-1-quic_jkona@quicinc.com/
>>>
>>> It might be an option to add this change right to the series,
>>> since it anyway requires a respin.
>>>
>>> A new compatible value "qcom,sm8650-cci" is NOT added to
>>> Documentation/devicetree/bindings/i2c/qcom,i2c-cci.yaml , because
>>> the controller IP description and selection is covered by a generic
>>> compatible value "qcom,msm8996-cci".
>>
>> You'll still need to add qcom,sm8650-cci to the "CCI v2" list in qcom,i2c-cci.yaml,
>> otherwise the DTBS check fail, even if the fallback is already present.
> 
> I do recognize the problem related to a build time warning, my motivation was
> to follow the rationale described in commit 3e383dce513f
> ("Revert "dt-bindings: i2c: qcom-cci: Document sc8280xp compatible"").
> 
> For a similar sc8280xp-cci case it was asked by Konrad to drop a new
> compatible, I kindly ask the reviewers and maintainers to stick to one
> of the two contradicting asks.

This is totally different, this commit added a new compatible that is used in the driver,
while here, you use a per-soc compatible that is (for now), only used in DT and uses
the generic "qcom,msm8996-cci" as a fallback because it is considered as beeing 99%
compatible and no software change is needed.

But having a per-soc compatible can help adding software support later in the case you
want to implement sm8650 specific features or add bug fixes.

It avoids changing the driver for no reason, and provides a backup in case there's
a driver change needed in the future that can be backported safely and still work
with older DT without changing the DT.

Neil

> 
> -- 
> Best wishes,
> Vladimir