On Thu, 2 May 2024 at 10:11, Peter Maydell <peter.mayd...@linaro.org> wrote: > On the QEMU side I guess we should strive to set up the MPIDR > fields to something plausibly matching the topology as defined > by the user on the command line. Unanswered questions: > > * I guess we need some kind of back-compat thing where for > old machine types we continue to report the old MPIDR > * what are the constraints on the Aff* fields (eg that kernel > commit suggests Aff0 shouldn't be > 15)?
This one is apparently related to GICv3 -- if the GIC doesn't implement RangeSelector support in ICC_SGI0R_EL1 and other places (advertised via GICD_TYPER.RSS and ICC_CTLR_EL1.SS) then there's no way to send an SGI to a CPU whose Aff0 is outside [0..15], and so you shouldn't build a system with Aff0 > 15. QEMU's GICv3 doesn't implement the RSS functionality (though it wouldn't be hard to add if we really cared), so we should also keep Aff0 in [0..15]. We have ARM_DEFAULT_CPUS_PER_CLUSTER = 8, which does keep us in that range. I don't think there's really a good reason for it to be 8 rather than 16: this might be legacy from GICv2? -- PMM
