Re: [PATCH] perf: arm_spe: Support heterogeneous ACPI systems

[Leo Yan <leo.yan@arm.com>]

On Fri, Oct 16, 2026 at 11:24:23AM +0800, Johnny Fan wrote:
> On Thu, Oct 15, 2026 at 03:19:26PM +0100, Leo Yan wrote:
> > The SPE driver probes its capabilities on one CPU selected by
> > smp_call_function_any(), then performs local setup on every CPU in
> > supported_cpus. It therefore relies on that mask being accurate;
> > including a CPU without SPE could lead to accesses to unimplemented
> > SPE system registers.
> 
> Right. On ACPI the driver gets no affinity information for this
> device, so supported_cpus falls back to cpu_possible_mask. That only
> works today because registration is limited to homogeneous systems.
> The PMSVer trimming in this patch works around the heterogeneous case;
> with the mask taken from the MADT walk, both go away.

SPE driver supports heterogeneous systems. If firmware creates proper
devices based on CPU topology, the driver can probe multiple instances.

So "registration is limited to homogeneous systems" is not quite right.

Thanks,
Leo