linux-kernel - [PATCH 2/5] dma-mapping: move the dma_get_sgtable API comments from arm to common code

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Message-Id: <20190725063401.29904-3-hch@lst.de>
Date:   Thu, 25 Jul 2019 08:33:58 +0200
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Takashi Iwai <tiwai@...e.de>, Robin Murphy <robin.murphy@....com>,
        Michal Simek <monstr@...str.eu>,
        linux-arm-kernel@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, linux-parisc@...r.kernel.org,
        linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] dma-mapping: move the dma_get_sgtable API comments from arm to common code

The comments are spot on and should be near the central API, not just
near a single implementation.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 arch/arm/mm/dma-mapping.c | 11 -----------
 kernel/dma/mapping.c      | 11 +++++++++++
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 6774b03aa405..4410af33c5c4 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -877,17 +877,6 @@ static void arm_coherent_dma_free(struct device *dev, size_t size, void *cpu_add
 	__arm_dma_free(dev, size, cpu_addr, handle, attrs, true);
 }
 
-/*
- * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems
- * that the intention is to allow exporting memory allocated via the
- * coherent DMA APIs through the dma_buf API, which only accepts a
- * scattertable.  This presents a couple of problems:
- * 1. Not all memory allocated via the coherent DMA APIs is backed by
- *    a struct page
- * 2. Passing coherent DMA memory into the streaming APIs is not allowed
- *    as we will try to flush the memory through a different alias to that
- *    actually being used (and the flushes are redundant.)
- */
 int arm_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
 		 void *cpu_addr, dma_addr_t handle, size_t size,
 		 unsigned long attrs)
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index b945239621d8..4ceb5b9016d8 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -136,6 +136,17 @@ int dma_common_get_sgtable(struct device *dev, struct sg_table *sgt,
 	return ret;
 }
 
+/*
+ * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems
+ * that the intention is to allow exporting memory allocated via the
+ * coherent DMA APIs through the dma_buf API, which only accepts a
+ * scattertable.  This presents a couple of problems:
+ * 1. Not all memory allocated via the coherent DMA APIs is backed by
+ *    a struct page
+ * 2. Passing coherent DMA memory into the streaming APIs is not allowed
+ *    as we will try to flush the memory through a different alias to that
+ *    actually being used (and the flushes are redundant.)
+ */
 int dma_get_sgtable_attrs(struct device *dev, struct sg_table *sgt,
 		void *cpu_addr, dma_addr_t dma_addr, size_t size,
 		unsigned long attrs)
-- 
2.20.1