[RFC PATCH 2/7] iommu: Add share domain interface in iommu for spimdev

[Tian, Kevin]

> From: Kenneth Lee
> Sent: Thursday, August 2, 2018 12:16 PM
> 
> On Thu, Aug 02, 2018 at 03:17:03AM +0000, Tian, Kevin wrote:
> > > From: Kenneth Lee
> > > Sent: Wednesday, August 1, 2018 6:22 PM
> > >
> > > From: Kenneth Lee <liguozhu at hisilicon.com>
> > >
> > > This patch add sharing interface for a iommu_group. The new interface:
> > >
> > > 	iommu_group_share_domain()
> > > 	iommu_group_unshare_domain()
> > >
> > > can be used by some virtual iommu_group (such as iommu_group for
> > > spimdev)
> > > to share their parent's iommu_group.
> > >
> > > When the domain of the group is shared, it cannot be changed before
> > > unshared.  In the future, notification can be added if update is required.
> >
> > Is it necessary or just asking VFIO to use parent domain directly?
> >
> Even we add to VFIO, the iommu still need to be changed. We can move
> the type1
> part to VFIO if we have agreement in RFC stage.

We have similar consideration in IOMMU aware mdev series. Now
we are inclined to avoid faked entity within IOMMU layer - leave to
caller to figure out right physical entity for any IOMMU ops. That 
might be leveraged here too after we get a new version.

Thanks
Kevin