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

[Dmitry Baryshkov]

On Tue, Dec 03, 2024 at 08:33:46PM +0530, Jagadeesh Kona wrote:
> 
> 
> 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().

It should be set, but then it should get the limited CPU mask rather
than the full CPU set. Isn't that enough for your case?

-- 
With best wishes
Dmitry