Re: [PATCH kernel] powerpc/iommu: Add iommu_ops to report capabilities and allow blocking domains

On Fri, Jul 08, 2022 at 11:32:58PM +1000, Alexey Kardashevskiy wrote:

quoted

For power the default domain should be NULL

NULL means that the platform is using the group to provide its DMA
ops. IIRC this patch was already setup correctly to do this?

The transition from NULL to blocking must isolate the group so all DMA
is blocked. blocking to NULL should re-estbalish platform DMA API
control.

The default domain should be non-NULL when the normal dma-iommu stuff is
providing the DMA API.

So, I think it is already setup properly, it is just the question of
what to do when entering/leaving blocking mode.

Well, the patch calls iommu_probe_device() which calls
iommu_alloc_default_domain() which creates IOMMU_DOMAIN_BLOCKED
(==0) as

Yes, we always create a blocking domain during probe, but it isn't
used until required

nothing initialized iommu_def_domain_type. Need a different default type
(and return NULL when IOMMU API tries creating this type)?

iommu_alloc_default_domain() should fail on power because none of the
domain types it tries to create are supported. This should result in a
NULL group->default_domain

Jason