powerpc: Fix the NUMA domain list on powernv

[jhibbits]

Summary

Consolidate the NUMA associativity handling into a platform function.
Non-NUMA platforms will just fall back to the default (0). Currently
only implemented for powernv, which uses a lookup table to map the
device tree associativity into a system NUMA domain.

Fixes hangs on powernv after r356534, and corrects a fairly longstanding
bug in powernv's NUMA handling, which ended up using domains 1 and 2 for
devices and memory on power9, while CPUs were bound to domains 0 and 1.

[luporl]

sys/powerpc/powernv/platform_powernv.c

154–157

'platform_associativity' (static) isn't being used anywhere in this file

'refpoints' is not used anywhere in this function.

Empty if block?

Maybe is there some code missing here?

532

Not sure, but shouldn't we use an index from refpoints here, instead of always 3 in associativity[]?

[jhibbits]

sys/powerpc/powernv/platform_powernv.c

154–157

I was trying several things in this. I meant to delete this finally, and revisit it later, but I'll use it instead.

532

Yes, I was going to just leave it as parity with the existing code, but I'll do single-level NUMA (index 0) for now. We should revisit it again at some point, to handle multi-level NUMA, but I don't think FreeBSD in general supports that yet.

[jhibbits]

Address @luporl's feedback, improving correctness.

[bdragon]

Looks good to me too. Thanks for putting this together!