gic-v2 and SGI interrupts on boot CPU

[Dmitry Skorodumov]

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.

Dmitry