[PATCH] arm64: topology: add MPIDR-based detection

[Lorenzo Pieralisi]

On Thu, Aug 21, 2014 at 06:15:40AM +0100, Zi Shen Lim wrote:
> Hi Ganapatrao,
> 
> On Tue, Aug 19, 2014 at 11:08 PM, Ganapatrao Kulkarni
> <gpkulkarni at gmail.com> wrote:
> > Hi Lorenzo,
> >
> > On Tue, Aug 19, 2014 at 4:06 AM, Lorenzo Pieralisi
> > <lorenzo.pieralisi at arm.com> wrote:
> >> On Mon, Aug 18, 2014 at 08:39:48AM +0100, Ganapatrao Kulkarni wrote:
> >>> How we map non SMT (MT bit24=0) cores of dual/multi socket system with
> >>> the topology which is using only aff0 and aff1?
> >>> can we use aff2  ( or concatenating aff2 and aff3)  to represent socket-id?
> >>
> >> Can you provide us with a description of the topology and the MPIDR_EL1
> >> list please ?
> >>
> >> I think that DT squashes the levels above cluster so that's how it could
> >> be implemented but first I would like to see what s the CPUs layout
> >> of the system.
> >
> > Our Soc has 48 core(Cavium's  thunderX) design. 48 cores are
> > sub-grouped in to 3 clusters.
> > In turn each cluster is having 16 cores.
> > We do have support for connecting 2 SoCs and making single system of 96 cores.
> >
> > the MPIDR mapping for this topology is,
> >
> > Aff0 is mapped to 16 cores within a cluster. Valid range is 0 to 0xf
> > Aff1 is mapped to cluster number, valid values are 0,1 and 2.
> > Aff2 is mapped to Socket-id or SoC number. Valid values are 0 and 1.
> 
> So, we went back and forth a few times and finally settled on what's
> merged into 3.17, due to lack of visibility into hardware that'll be
> shipped.
> 
> At one point, we had something approximating behavior of DT-based
> topology, along the lines of:
> 
>         if (mpidr & MPIDR_MT_BITMASK) {
>                 /* Multiprocessor system : Multi-threads per core */
>                 cpuid_topo->thread_id  = MPIDR_AFFINITY_LEVEL(mpidr, 0);
>                 cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 1);
>                 cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 2) |
>                                          MPIDR_AFFINITY_LEVEL(mpidr, 3) << 8;
>         } else {
>                 /* Multiprocessor system : Single-thread per core */
>                 cpuid_topo->thread_id  = -1;
>                 cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 0);
>                 cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 1) |
>                                          MPIDR_AFFINITY_LEVEL(mpidr, 2) << 8 |
>                                          MPIDR_AFFINITY_LEVEL(mpidr, 3) << 16;
>         }
> 
> BTW, Mark Brown just posted "[PATCH] arm64: topology: Fix handling of
> multi-level cluster MPIDR-based detection" which reintroduces the
> above, albeit only for MT case.
> 
> I suspect you're looking for something above for the non-MT case?
> As a workaround, have you considered defining your topology in DT?
> 
> Lorenzo,
> 
> Are you open to the above "workaround" given that Thunder is facing
> the current deficiency for non-MT case?
> Or is it time to introduce socket_id or something equivalent?

Well, we have to do something for certain, I think M. Brown's patch
seems a reasonable solution to this problem, I will give it more thought
and come back to you beginning of September (I am currently on holiday).

Thank you,
Lorenzo