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

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Message-ID: <cab2be55-2ea4-4bca-a574-eb6800cc38f1@arm.com>
Date: Tue, 3 Feb 2026 09:44:07 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.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 03/02/2026 09:36, Konrad Dybcio wrote:
> 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

Do you mean, same IP block integrated to different SoC ? Or are they
different implementations altogether ? Why are these not applicable for
other components ? (e.g., Tnoc, I-Tnoc, TPDA, TPDM etc ?)

> 
> 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

Fair enough, thank for the explanation.

Kind regards
Suzuki

> 
> 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