From: Jeremy Gebben <>

In the ARM SMMU architecture, pagetable programming is controlled
by the TTBR0 register. The layout of this
registers varies depending on the pagetable format in use.
In particular, the ASID (address space ID) field is found in
CONTEXTIDR when using V7S format and in the top bits of TTBR0
for V7L and V8L.

Some drivers need to program hardware to switch domains on the
fly. This attribute allows the correct setting to be determined
by querying the domain rather than directly reading registers and
making assumptions about the pagetable format. The domain must be
attached before TTBR0 may be queried.

Signed-off-by: Jeremy Gebben <>
Signed-off-by: Jordan Crouse <>
 include/linux/iommu.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index d537cc9..544cfc6 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -115,6 +115,7 @@ enum iommu_attr {
        DOMAIN_ATTR_NESTING,    /* two stages of translation */

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