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

[Zi Shen Lim]

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?