Re: [PATCH V6 3/4] dt-bindings: interconnect: Add generic compatible qcom,epss-l3-perf

[Krzysztof Kozlowski <krzk@kernel.org>]

On 27/11/2024 19:49, Dmitry Baryshkov wrote:
> On 27 November 2024 20:27:27 EET, Krzysztof Kozlowski <krzk@kernel.org> wrote:
>> On 27/11/2024 17:53, Dmitry Baryshkov wrote:
>>> On Wed, Nov 27, 2024 at 08:23:04AM -0600, Rob Herring wrote:
>>>> On Mon, Nov 25, 2024 at 05:45:10PM +0000, Raviteja Laggyshetty wrote:
>>>>> EPSS instance on sc7280, sm8250 SoCs, use PERF_STATE register instead of
>>>>> REG_L3_VOTE to scale L3 clocks, hence adding a new generic compatible
>>>>> "qcom,epss-l3-perf" for these targets.
>>>>
>>>> Is this a h/w difference from prior blocks or you just want to use B 
>>>> instead of A while the h/w has both A and B? The latter sounds like 
>>>> driver policy.
>>>>
>>>> It is also an ABI break for s/w that didn't understand 
>>>> qcom,epss-l3-perf.
>>>
>>> As the bindings keep old compatible strings in addition to the new
>>> qcom,epss-l3-perf, where is the ABI break? Old SW will use old entries,
>>> newer can use either of those.
>> No, this change drops qcom,epss-l3 and adds new fallback. How old
>> software can work in such case? It's broken.
> 
> Oh, I see. We had a platform-specific overrides for those two. Then I think we should completely drop the new qcom,epss-l3-perf idea and follow the sm8250 / sc7280 example. This means compatible = "qcom,sa8775p-perf", "qcom,epss-l3". 

It depends for example whether epss-l3 is valid at all. ABI is not
broken if nothing was working in the first place, assuming it is
explained in commit msg (not the case here).

Best regards,
Krzysztof