On Wed, Aug 04, 2021 at 11:07:42AM -0300, Jason Gunthorpe wrote:

On Tue, Aug 03, 2021 at 11:58:54AM +1000, David Gibson wrote:

quoted

quoted

I'd rather deduce the endpoint from a collection of devices than the
other way around...

Which I think is confusing, and in any case doesn't cover the case of
one "device" with multiple endpoints.

Well they are both confusing, and I'd prefer to focus on the common
case without extra mandatory steps. Exposing optional endpoint sharing
information seems more in line with where everything is going than
making endpoint sharing a first class object.

AFAIK a device with multiple endpoints where those endpoints are
shared with other devices doesn't really exist/or is useful? Eg PASID
has multiple RIDs by they are not shared.

No, I can't think of a (non-contrived) example where a device would
have *both* multiple endpoints and those endpoints are shared amongst
multiple devices.  I can easily think of examples where a device has
multiple (non shared) endpoints and where multiple devices share a
single endpoint.

The point is that making endpoints explicit separates the various
options here from the logic of the IOMMU layer itself.  New device
types with new possibilities here means new interfaces *on those
devices*, but not new interfaces on /dev/iommu.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson