[PATCH v9 06/11] ACPI/IORT: Add support to retrieve IORT RMR reserved regions

[Christoph Hellwig]

On Thu, Apr 07, 2022 at 02:53:38PM +0100, Robin Murphy wrote:
> > Why can't this just go into generic_iommu_put_resv_regions?  The idea
> > that the iommu low-level drivers need to call into dma-iommu which is
> > a consumer of the IOMMU API is odd.  Especially if that just calls out
> > to ACPI code and generic IOMMU code only anyway.
> 
> Because assuming ACPI means IORT is not generic. Part of the aim in adding
> the union to iommu_resv_region is that stuff like AMD's unity_map_entry and
> Intel's dmar_rmrr_unit can be folded into it as well, and their reserved
> region handling correspondingly simplified too.
> 
> The iommu_dma_{get,put}_resv_region() helpers are kind of intended to be
> specific to the fwnode mechanism which deals with IORT and devicetree (once
> the reserved region bindings are fully worked out).

But IORT is not driver₋specific code.  So we'll need a USE_IORT flag
somewhere in core IOMMU code instead of trying to stuff this into
driver operations.  and dma-iommu mostly certainly implies IORT even
less than ACPI.