> From: Jason Gunthorpe <jgg@xxxxxxxx>
> Sent: Tuesday, July 5, 2022 8:49 AM
>
> On Fri, Jul 01, 2022 at 07:10:45AM +0000, Tian, Kevin wrote:
> > > From: Alexey Kardashevskiy <aik@xxxxxxxxx>
> > > Sent: Friday, July 1, 2022 2:18 PM
> > >
> > > VFIO on POWER does not implement iommu_ops and therefore
> > > iommu_capable()
> > > always returns false and __iommu_group_alloc_blocking_domain()
> always
> > > fails.
> > >
> > > iommu_group_claim_dma_owner() in setting container fails for the same
> > > reason - it cannot allocate a domain.
> > >
> > > This skips the check for platforms supporting VFIO without implementing
> > > iommu_ops which to my best knowledge is POWER only.
> > >
> > > This also allows setting container in absence of iommu_ops.
> > >
> > > Fixes: 70693f470848 ("vfio: Set DMA ownership for VFIO devices")
> > > Fixes: e8ae0e140c05 ("vfio: Require that devices support DMA cache
> > > coherence")
> > > Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> > > ---
> > >
> > > Not quite sure what the proper small fix is and implementing iommu_ops
> > > on POWER is not going to happen any time soon or ever :-/
> >
> > I'm not sure how others feel about checking bus->iommu_ops outside
> > of iommu subsystem. This sounds a bit non-modular to me and it's not
> > obvious from the caller side why lacking of iommu_ops implies the two
> > relevant APIs are not usable.
>
> The more I think about this, the more I think POWER should implement
> partial iommu_ops to make this work. It would not support an UNMANAGED
> domain, or default domains, but it would support blocking and the
> coherency probe.
Yes, this sounds a better approach.
>
> This makes everything work properly and keeps the mess out of the core
> code.
>
> It should not be hard to do if someone can share a bit about the ppc
> code and test it..
>
> Jason
