iommu/io-pgtable-arm: Centralise sync points

With all current users now opted in to DMA API operations, make the
iommu_dev pointer mandatory, rendering the flush_pgtable callback
redundant for cache maintenance. However, since the DMA calls could be
nops in the case of a coherent IOMMU, we still need to ensure the page
table updates are fully synchronised against a subsequent page table
walk. In the unmap path, the TLB sync will usually need to do this
anyway, so just cement that requirement; in the map path which may
consist solely of cacheable memory writes (in the coherent case),
insert an appropriate barrier at the end of the operation, and obviate
the need to call flush_pgtable on every individual update for
synchronisation.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
[will: slight clarification to tlb_sync comment]
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/iommu/io-pgtable.h b/drivers/iommu/io-pgtable.h
index c69529c78914..e8fadb012ed2 100644
--- a/drivers/iommu/io-pgtable.h
+++ b/drivers/iommu/io-pgtable.h
@@ -17,7 +17,9 @@ enum io_pgtable_fmt {
  *
  * @tlb_flush_all: Synchronously invalidate the entire TLB context.
  * @tlb_add_flush: Queue up a TLB invalidation for a virtual address range.
- * @tlb_sync:      Ensure any queue TLB invalidation has taken effect.
+ * @tlb_sync:      Ensure any queued TLB invalidation has taken effect, and
+ *                 any corresponding page table updates are visible to the
+ *                 IOMMU.
  * @flush_pgtable: Ensure page table updates are visible to the IOMMU.
  *
  * Note that these can all be called in atomic context and must therefore