powerpc64: change CAS to support Radix MMU

[luporl]

Summary

Use radix_mmu environment variable to select between Hash or Radix MMU, when performing the CAS method call.

This matches kernel's behavior, by selecting Hash MMU by default and Radix if radix_mmu is not zero, to make sure that both loader and kernel always select the same MMU.

If the detected CPU is not a POWER9, then Hash MMU is selected, regardless of radix_mmu value, as in kernel.

Test Plan

Tested on QEMU pseries with KVM, selecting both Hash and Radix MMUs.

[jhibbits]

stand/powerpc/ofw/cas.c

240

Defaulting off for radix_mmu, even on power9?

[luporl]

stand/powerpc/ofw/cas.c

240

Yes, we are holding making radix default because of D31232. BTW, do you think it is ok to commit it already?

When it lands, there is already D30797 to make radix default. Then we can just get back here and make it default in loader too.

[jhibbits]

stand/powerpc/ofw/cas.c

240

That's all I wanted to know, thanks!

[luporl]

Query device tree for Radix/GTSE support, instead of using CPU version and HV bit checks, as this is a better approach, as discussed in IRC.

[luporl]

Add missing break

[jhibbits]

stand/powerpc/ofw/cas.c

32–33

Why not make this a #ifdef instead?

[luporl]

Address reviewer's comments

[luporl]

stand/powerpc/ofw/cas.c

32–33

Ok, I've used #if just because it's a bit less typing to enable/disable it.

[jhibbits]

Don't forget to update the commit message, with the latest changes you made.