linux-kernel - Re: [PATCH 1/3] dt-binding: document QCOM platforms for CTCU device

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Message-ID: <a74b8e61-6e15-400a-a7aa-d589f3545421@oss.qualcomm.com>
Date: Tue, 3 Feb 2026 10:36:41 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
        Jie Gan <jie.gan@....qualcomm.com>, Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@...aro.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Tingwei Zhang <tingwei.zhang@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-binding: document QCOM platforms for CTCU device

On 2/3/26 10:31 AM, Suzuki K Poulose wrote:
> On 03/02/2026 09:00, Jie Gan wrote:
>>
>>
>> On 2/3/2026 4:50 PM, Konrad Dybcio wrote:
>>> On 2/3/26 9:08 AM, Jie Gan wrote:
>>>> Document the platforms that fallback to using the qcom,sa8775p-ctcu
>>>> compatible for probing.
>>>>
>>>> Signed-off-by: Jie Gan <jie.gan@....qualcomm.com>
>>>> ---
>>>>   Documentation/devicetree/bindings/arm/qcom,coresight-ctcu.yaml | 4 ++++
>>>>   1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/arm/qcom,coresight- ctcu.yaml b/Documentation/devicetree/bindings/arm/qcom,coresight- ctcu.yaml
>>>> index e002f87361ad..68853db52bef 100644
>>>> --- a/Documentation/devicetree/bindings/arm/qcom,coresight-ctcu.yaml
>>>> +++ b/Documentation/devicetree/bindings/arm/qcom,coresight-ctcu.yaml
>>>> @@ -29,6 +29,10 @@ properties:
>>>>       oneOf:
>>>>         - items:
>>>>             - enum:
>>>> +              - qcom,glymur-ctcu
>>>> +              - qcom,hamoa-ctcu
>>>> +              - qcom,kaanapali-ctcu
>>>> +              - qcom,pakala-ctcu
>>>
>>> Platforms with existing numeric compatibles should continue to use them,
>>> so that the mess is somewhat containable
>>
>> Sure Konrad. So for Pakala, I will change it back to qcom,sm8750-ctcu
> 
> Why do we need different compatibles for the others ? Are they not all compliant to the CTCU programming model ? i.e., sa8775p-ctcu ? or even,
> a generic,
> 
> qcom,coresight-ctcu

It's a huge anti-pattern with the DT maintainers, since a compatible is
the only way to effectively differentiate different implementations (i.e.
instances on different SoCs) of an IP block

This is important for the case where a DTB is shipped as part of firmware
and can not be replaced - if some quirk needs to be applied retroactively,
we can look for "qcom,glymur-ctcu" without affecting all the 50 other'
users of the effectively-identical IP block

In this case, we're already reducing the impact on the driver, as that
only looks for the single fallback compatible (qcom,sa8775p-ctcu)

Konrad