Re: [PATCH v1 3/8] iommu: Extend iommu_at[de]tach_device() for multi-device groups

[Joerg Roedel]

On Mon, Feb 14, 2022 at 09:03:13AM -0400, Jason Gunthorpe wrote:
> Groups should disappear into an internal implementation detail, not be
> so prominent in the API.

Not going to happen, IOMMU groups are ABI and todays device assignment
code, including user-space, relies on them.

Groups implement and important aspect of hardware IOMMUs that the API
can not abstract away: That there are devices which share the same
request-id. 

This is not an issue for devices concerned by iommufd, but for legacy
device assignment it is. The IOMMU-API needs to handle both in a clean
API, even if it means that drivers need to lookup the sub-group of a
device first.

And I don't see how a per-device API can handle both in a device-centric
way. For sure it is not making it 'device centric but operate on groups
under the hood'.

Regards,

	Joerg