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

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Message-ID: <91f23c5d-0bc1-49e4-9b7a-85120732326f@quicinc.com>
Date: Thu, 26 Dec 2024 21:26:16 +0530
From: Raviteja Laggyshetty <quic_rlaggysh@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Krzysztof Kozlowski
	<krzk@...nel.org>, Rob Herring <robh@...nel.org>
CC: Georgi Djakov <djakov@...nel.org>,
        Krzysztof Kozlowski
	<krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Odelu Kukatla
	<quic_okukatla@...cinc.com>,
        Mike Tipton <quic_mdtipton@...cinc.com>,
        "Sibi
 Sankar" <quic_sibis@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V6 3/4] dt-bindings: interconnect: Add generic compatible
 qcom,epss-l3-perf



On 11/28/2024 1:15 AM, Dmitry Baryshkov wrote:
> On 27 November 2024 21:22:02 EET, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>> On 27/11/2024 19:49, Dmitry Baryshkov wrote:
>>> On 27 November 2024 20:27:27 EET, Krzysztof Kozlowski <krzk@...nel.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).
> 
> Judging by the current schema, epss-l3 is defined as new HW block of aka not OSM L3, no matter which register is used for programming.
> 

I am going to remove the newly added "qcom,epss-l3-perf" compatible and
add target specific compatible "qcom,sa8775p-epss-l3" along with
existing generic "qcom,epss-l3" compatible.
> 
>>
>> Best regards,
>> Krzysztof
>