linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: sa8775p: Add CPU OPP tables to scale DDR/L3

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Message-ID: <d78e6fc9-2238-4f55-a604-f60df8565166@quicinc.com>
Date: Tue, 3 Dec 2024 20:33:46 +0530
From: Jagadeesh Kona <quic_jkona@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>
CC: Brian Masney <bmasney@...hat.com>, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Ajit Pandey <quic_ajipan@...cinc.com>,
        "Imran
 Shaik" <quic_imrashai@...cinc.com>,
        Taniya Das <quic_tdas@...cinc.com>,
        "Satya Priya Kakitapalli" <quic_skakitap@...cinc.com>,
        Shivnandan Kumar
	<quic_kshivnan@...cinc.com>
Subject: Re: [PATCH 2/3] arm64: dts: qcom: sa8775p: Add CPU OPP tables to
 scale DDR/L3



On 11/30/2024 8:02 PM, Konrad Dybcio wrote:
> On 14.11.2024 11:48 PM, Dmitry Baryshkov wrote:
>> On Mon, Nov 11, 2024 at 06:39:48PM +0530, Jagadeesh Kona wrote:
>>>
>>>
>>> On 10/17/2024 9:12 PM, Brian Masney wrote:
>>>> On Thu, Oct 17, 2024 at 02:58:31PM +0530, Jagadeesh Kona wrote:
>>>>> +	cpu0_opp_table: opp-table-cpu0 {
>>>>> +		compatible = "operating-points-v2";
>>>>> +		opp-shared;
>>>>> +
>>>>> +		cpu0_opp_1267mhz: opp-1267200000 {
>>>>> +			opp-hz = /bits/ 64 <1267200000>;
>>>>> +			opp-peak-kBps = <6220800 29491200>;
>>>>> +		};
>>>>> +
>>>>> +		cpu0_opp_1363mhz: opp-1363200000 {
>>>>> +			opp-hz = /bits/ 64 <1363200000>;
>>>>> +			opp-peak-kBps = <6220800 29491200>;
>>>>> +		};
>>>>
>>>> [snip]
>>>>
>>>>> +	cpu4_opp_table: opp-table-cpu4 {
>>>>> +		compatible = "operating-points-v2";
>>>>> +		opp-shared;
>>>>> +
>>>>> +		cpu4_opp_1267mhz: opp-1267200000 {
>>>>> +			opp-hz = /bits/ 64 <1267200000>;
>>>>> +			opp-peak-kBps = <6220800 29491200>;
>>>>> +		};
>>>>> +
>>>>> +		cpu4_opp_1363mhz: opp-1363200000 {
>>>>> +			opp-hz = /bits/ 64 <1363200000>;
>>>>> +			opp-peak-kBps = <6220800 29491200>;
>>>>> +		};
>>>>
>>>> There's no functional differences in the cpu0 and cpu4 opp tables. Can
>>>> a single table be used?
>>>>
>>>> This aligns with my recollection that this particular SoC only has the
>>>> gold cores.
>>>>
>>>> Brian
>>>>
>>>
>>> Thanks Brian for your review. Sorry for the delayed response.
>>>
>>> We require separate OPP tables for CPU0 and CPU4 to allow independent
>>> scaling of DDR and L3 frequencies for each CPU domain, with the final
>>> DDR and L3 frequencies being an aggregate of both.
>>>
>>> If we use a single OPP table for both CPU domains, then _allocate_opp_table() [1]
>>> won't be invoked for CPU4. As a result both CPU devices will end up in sharing
>>> the same ICC path handle, which could lead to one CPU device overwriting the bandwidth
>>> votes of other.
> 
> Oh that's a fun find.. clocks get the same treatment.. very bad,
> but may explain some schroedingerbugs.
> 
> Taking a peek at some code paths, wouldn't dropping opp-shared
> solve our issues? dev_pm_opp_set_sharing_cpus() overrides it
> 
> Konrad

Thanks Konrad for your review.

Yes, correct. I tried dropping opp-shared but it is again getting set due to
dev_pm_opp_set_sharing_cpus().

Thanks,
Jagadeesh