Mandate IOMMU RIMT (ACPI) requirement

[andreiw]

AFAICT Server SoC mandates IOMMU
BRS has non-normative text about RIMT on systems supporting IOMMU

...need requirement in this spec to tie it together.

[andreiw]

Actually such a text could well be in the BRS document, but isn't (along with many other requirements that are implicit in the ACPI spec and dependent specs).

So do we really need the RIMT text (i.e. if you have an IOMMU, you will expose it via RIMT). Why would IOMMU get this treatment and something else (AIA) would not?

[andreiw]

The thought here is that ACPI doesn't actually require a RIMT for a RISC-V compliant IOMMU.

[andreiw]

The BRS does not really have normative text around the RIMT. A solution could be to make RIMT spec one of the BRS-I dependencies (and ensure RIMT has text that requires implementation if a compliant RISC-V IOMMU is present)