gic-v2 and SGI interrupts on boot CPU

[Michael Tuexen]

> On 21. Apr 2021, at 00:02, Dmitry Skorodumov via freebsd-arm <freebsd-arm at freebsd.org> wrote:
> 
> Hi
> 
> 
> It looks like code for gic-v2 in FreeBSD not quite correctly relies on implementation defined behaviour of GIC.
> 
> The  g<file:///Users/sdmitry/Downloads/IHI0048B_b_gic_architecture_specification.pdf>ic 2.0 spec https://developer.arm.com/documentation/ihi0048/bb chapter 3.2.2 "Interrupt controls in the GIC" states the following:
> 
> "Whether SGIs are permanently enabled, or can be enabled and disabled by writes to the GICD_ISENABLERn and GICD_ICENABLERn, is IMPLEMENTATION DEFINED."
> 
> But code in sys/arm/arm/gic.c assumes that SGI are always enabled and doesn't configure them at initialization. They are initialized only for secondary CPUs - in arm_gic_init_secondary().
> 
> For sure it is a rather minor issue, since all appears to be ok in gic-v3 (v3 code enables SGIs for all CPUs, including the boot one). And even if platform supports only gic-v2, likely SGIs are always enabled anyway. So, my post is rather pedantic notice without real life case.
Dear all,

if I understand things correctly, the problem described is the cause which does not
allow to use more than one CPU core in FreeBSD when running on Parallels Desktop on
an M1 based Mac. It runs perfectly well with one core, but with multiple cores it
locks up during boot.

It would be great if some could propose a patch. I would be more than happy to test it.

Best regards
Michael
> 
> Dmitry
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