[PATCH v3 0/2] iommu: handle drivers that manage iommu directly

[Will Deacon]

On Tue, Sep 10, 2019 at 10:10:49AM -0700, Rob Clark wrote:
> On Tue, Sep 10, 2019 at 9:34 AM Robin Murphy <robin.murphy at arm.com> wrote:
> > On 06/09/2019 22:44, Rob Clark wrote:
> > > NOTE that in discussion of previous revisions, RMRR came up.  This is
> > > not really a replacement for RMRR (nor does RMRR really provide any
> > > more information than we already get from EFI GOP, or DT in the
> > > simplefb case).  I also don't see how RMRR could help w/ SMMU handover
> > > of CB/SMR config (Bjorn's patchset[1]) without defining new tables.
> >
> > The point of RMRR-like-things is that they identify not just the memory
> > region but also the specific device accessing them, which means the
> > IOMMU driver knows up-front which IDs etc. it must be careful not to
> > disrupt. Obviously for SMMU that *would* be some new table (designed to
> > encompass everything relevant) since literal RMRRs are specifically an
> > Intel VT-d thing.
> 
> Perhaps I'm not looking in the right place, but the extent of what I
> could find about RMRR tables was:
> 
> https://github.com/tianocore/edk2/blob/master/MdePkg/Include/IndustryStandard/DmaRemappingReportingTable.h#L122
> 
> I couldn't really see how that specifies the device.  But entirely
> possible that I'm not seeing the whole picture.

I don't think anybody was planning to implement RMRR "as-is" for arm64, so
you might be better off looking at the proposal from Thierry, although it
has some issues that are still to be resolved:

http://lkml.kernel.org/r/20190829111407.17191-1-thierry.reding@gmail.com

Will