linux-kernel - [PATCH] arm64: Add support for DMA_ATTR_SKIP_CPU

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Date:   Wed, 11 Jan 2017 11:11:17 +0100
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Robin Murphy <robin.murphy@....com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Takeshi Kihara <takeshi.kihara.df@...esas.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] arm64: Add support for DMA_ATTR_SKIP_CPU_SYNC attribute to swiotlb

From: Takeshi Kihara <takeshi.kihara.df@...esas.com>

This patch adds support for DMA_ATTR_SKIP_CPU_SYNC attribute for
dma_{un}map_{page,sg} functions family to swiotlb.

DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of
the CPU cache for the given buffer assuming that it has been already
transferred to 'device' domain.

Ported from IOMMU .{un}map_{sg,page} ops.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@...esas.com>
Acked-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
v2:
  - Add Acked-by.

Support for DMA_ATTR_SKIP_CPU_SYNC was included when porting the IOMMU
ops from arm to arm64 in commit 13b8629f651164d7 ("arm64: Add IOMMU
dma_ops").

Presumably it was an oversight that the existing swiotlb based
implementation didn't have support for DMA_ATTR_SKIP_CPU_SYNC yet?
---
 arch/arm64/mm/dma-mapping.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index e04082700bb16c35..1d7d5d2881db7c19 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -211,7 +211,8 @@ static dma_addr_t __swiotlb_map_page(struct device *dev, struct page *page,
 	dma_addr_t dev_addr;
 
 	dev_addr = swiotlb_map_page(dev, page, offset, size, dir, attrs);
-	if (!is_device_dma_coherent(dev))
+	if (!is_device_dma_coherent(dev) &&
+	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
 		__dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
 
 	return dev_addr;
@@ -222,7 +223,8 @@ static void __swiotlb_unmap_page(struct device *dev, dma_addr_t dev_addr,
 				 size_t size, enum dma_data_direction dir,
 				 unsigned long attrs)
 {
-	if (!is_device_dma_coherent(dev))
+	if (!is_device_dma_coherent(dev) &&
+	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
 		__dma_unmap_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
 	swiotlb_unmap_page(dev, dev_addr, size, dir, attrs);
 }
@@ -235,7 +237,8 @@ static int __swiotlb_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
 	int i, ret;
 
 	ret = swiotlb_map_sg_attrs(dev, sgl, nelems, dir, attrs);
-	if (!is_device_dma_coherent(dev))
+	if (!is_device_dma_coherent(dev) &&
+	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
 		for_each_sg(sgl, sg, ret, i)
 			__dma_map_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
 				       sg->length, dir);
@@ -251,7 +254,8 @@ static void __swiotlb_unmap_sg_attrs(struct device *dev,
 	struct scatterlist *sg;
 	int i;
 
-	if (!is_device_dma_coherent(dev))
+	if (!is_device_dma_coherent(dev) &&
+	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
 		for_each_sg(sgl, sg, nelems, i)
 			__dma_unmap_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
 					 sg->length, dir);
-- 
1.9.1