ARM: 8506/1: common: DMA-mapping: add DMA_ATTR_ALLOC_SINGLE_PAGES attribute

This patch adds the DMA_ATTR_ALLOC_SINGLE_PAGES attribute to the
DMA-mapping subsystem.

This attribute can be used as a hint to the DMA-mapping subsystem that
it's likely not worth it to try to allocate large pages behind the
scenes.  Large pages are likely to make an IOMMU TLB work more
efficiently but may not be worth it.  See the Documentation contained in
this patch for more details about this attribute and when to use it.

Note that the name of the hint (DMA_ATTR_ALLOC_SINGLE_PAGES) is loosely
based on the name MADV_NOHUGEPAGE.  Just as there is MADV_NOHUGEPAGE
vs. MADV_HUGEPAGE we could also add an "opposite" attribute to
DMA_ATTR_ALLOC_SINGLE_PAGES.  Without having the "opposite" attribute
the lack of DMA_ATTR_ALLOC_SINGLE_PAGES means "use your best judgement
about whether to use small pages or large pages".

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/dma-attrs.h b/include/linux/dma-attrs.h
index 99c0be00b47c..5246239a4953 100644
--- a/include/linux/dma-attrs.h
+++ b/include/linux/dma-attrs.h
@@ -18,6 +18,7 @@ enum dma_attr {
 	DMA_ATTR_NO_KERNEL_MAPPING,
 	DMA_ATTR_SKIP_CPU_SYNC,
 	DMA_ATTR_FORCE_CONTIGUOUS,
+	DMA_ATTR_ALLOC_SINGLE_PAGES,
 	DMA_ATTR_MAX,
 };