arm64: dma-mapping: optimize unmap coherency check
Change arm_iommu_unmap_page to check the DMA attributes for buffer
coherency support instead of checking the iommu page table.
This change now requires that clients correctly set the
DMA_ATTR_FORCE_COHERENT or DMA_ATTR_FORCE_NON_COHERENT DMA
attributes in their unmap call if they used it with their map call.
This will improve the performance of the arm_iommu_unmap_page
call.
Change-Id: Ie96ef0a1906a8732b7b1eef7bed8aa85abee95f4
Signed-off-by: Liam Mark <lmark@codeaurora.org>
diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index d534246..01e865d 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -182,6 +182,11 @@
When passed to a DMA map call the DMA_ATTR_FORCE_COHERENT DMA
attribute can be used to force a buffer to be mapped as IO coherent.
+
+When the DMA_ATTR_FORCE_COHERENT attribute is set during a map call ensure
+that it is also set during for the matching unmap call to ensure that the
+correct cache maintenance is carried out.
+
This DMA attribute is only currently supported for arm64 stage 1 IOMMU
mappings.
@@ -193,5 +198,10 @@
coherent.
The DMA_ATTR_FORCE_NON_COHERENT DMA attribute overrides the buffer IO
coherency configuration set by making the device IO coherent.
+
+When the DMA_ATTR_FORCE_NON_COHERENT attribute is set during a map call
+ensure that it is also set during for the matching unmap call to ensure
+that the correct cache maintenance is carried out.
+
This DMA attribute is only currently supported for arm64 stage 1 IOMMU
mappings.