On Wed, Dec 04, 2024 at 02:15:09PM +0530, Jagadeesh Kona wrote:
>
>
> On 12/4/2024 8:43 AM, Dmitry Baryshkov wrote:
> > 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?
> >
>
> Even if we call dev_pm_opp_set_sharing_cpus() with the limited CPU mask, it adds
> OPP_TABLE_ACCESS_SHARED flag to the OPP table. Due to this flag being set, if this
> same opp table is used for another CPU domain(CPU4-7) also in DT, then _managed_opp[1]
> which gets called inside from dev_pm_opp_of_add_table() for CPU4 will return the same
> CPU0 OPP table.
>
> Due to above, _allocate_opp_table() [2] won't be invoked for CPU4 but instead CPU4 will be
> added as device under the CPU0 OPP table [3]. Due to this, dev_pm_opp_of_find_icc_paths() [4]
> won't be invoked for CPU4 device and hence CPU4 won't be able to independently scale it's
> interconnects. Both CPU0 and CPU4 devices will scale the same ICC path which can lead to one
> device overwriting the BW vote placed by other device. So we need two separate OPP tables for
> both domains.
Ack, that makes sense. Thanks for the explanation!
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/opp/core.c#n1600
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/opp/core.c#n1613
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/opp/core.c#n1606
> [4] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/opp/core.c#n1484
>
> Thanks,
> Jagadeesh
--
With best wishes
Dmitry
