SPI MSI mapping for gic v3 acpi in arm64

[schakrabarti_microsoft.com]

Summary

Microsoft Azure Hyper-V uses SPI to map MSI in ARM64, instead of using LPI IDS.
To enable that we need to have gic registered with ACPI_MSI_XREF and gic acpi to map SPI for MSI.

[emaste]

sys/arm64/arm64/gic_v3.c

393

style(9) is four spaces for 2nd level indentation (i.e., arg line wrapping) so please leave this unchanged

[imp]

Are there times other than when running as a hyperv guest that these might be needed?

[schakrabarti_microsoft.com]

In D37763#862942, @imp wrote:

Are there times other than when running as a hyperv guest that these might be needed?

If any other ACPI platform uses SPI for MSI, instead of using LPI and ITS for MSI, then it would be required.

[andrew]

sys/arm64/arm64/gic_v3.c

385

Is this needed? We set the end in gic_v3_acpi.c

sys/arm64/arm64/gic_v3_acpi.c

339

range

[schakrabarti_microsoft.com]

sys/arm64/arm64/gic_v3.c

385

Yes, but the value of the end is 0 for Hyper-V, so if the end value is zero, we are using the full range.

[jrtc27]

sys/arm64/arm64/gic_v3_acpi.c

339

This was not addressed prior to committing

[whu]

sys/arm64/arm64/gic_v3_acpi.c

339

Will fix this typo in next commit.