Re: [PATCH V2 1/3] dt-bindings: interconnect: Add EPSS L3 compatible for SA8775P

[Konrad Dybcio]

On 4.11.2024 7:40 AM, Raviteja Laggyshetty wrote:
> 
> 
> On 11/1/2024 12:26 AM, Dmitry Baryshkov wrote:
>> On Wed, Oct 30, 2024 at 12:23:57PM +0530, Raviteja Laggyshetty wrote:
>>>
>>>
>>> On 10/26/2024 8:15 PM, Dmitry Baryshkov wrote:
>>>> On Sat, Oct 26, 2024 at 12:30:56PM +0000, Raviteja Laggyshetty wrote:
>>>>> Add Epoch Subsystem (EPSS) L3 interconnect provider binding on
>>>>> SA8775P SoCs.
>>>>>
>>>>> Signed-off-by: Raviteja Laggyshetty <quic_rlaggysh@xxxxxxxxxxx>
>>>>> ---
>>>>>  .../devicetree/bindings/interconnect/qcom,osm-l3.yaml         | 4 ++++
>>>>>  1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml b/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml
>>>>> index 21dae0b92819..042ca44c32ec 100644
>>>>> --- a/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml
>>>>> +++ b/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml
>>>>> @@ -34,6 +34,10 @@ properties:
>>>>>                - qcom,sm8250-epss-l3
>>>>>                - qcom,sm8350-epss-l3
>>>>>            - const: qcom,epss-l3
>>>>> +      - items:
>>>>> +          - enum:
>>>>> +              - qcom,sa8775p-epss-l3
>>>>> +          - const: qcom,epss-l3-perf
>>>>
>>>> Why is it -perf? What's so different about it?
>>>
>>> The EPSS instance in SA8775P uses PERF_STATE register instead of REG_L3_VOTE to scale L3 clocks.
>>> So adding new generic compatible "qcom,epss-l3-perf" for PERF_STATE register based l3 scaling.
>>
>> Neither sm8250 nor sc7280 use this compatible, while they also use
>> PERF_STATE register.
>>
> That is correct, both sm8250 and sc7280 use perf state register.
> The intention for adding "qcom,epss-l3-perf" generic compatible is to use it for the chipsets which use perf state register for l3 scaling.
> Using generic compatible avoids the need for adding chipset specific compatible in match table.

That is exactly what bindings guidelines forbid.

You need a SoC-specific compatible so that you can address platform-
specific quirks that may arise in the future while keeping backwards
compatibility with older device trees

Konrad