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From: Christoph Hellwig <hch@lst.de>
To: iommu@lists.linux-foundation.org,
	Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Vladimir Murzin <vladimir.murzin@arm.com>,
	Takashi Iwai <tiwai@suse.de>, Helge Deller <deller@gmx.de>,
	Robin Murphy <robin.murphy@arm.com>,
	Michal Simek <monstr@monstr.eu>,
	linux-arm-kernel@lists.infradead.org,
	linux-m68k@lists.linux-m68k.org, linux-parisc@vger.kernel.org,
	linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org,
	linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH 2/8] dma-mapping: move the dma_get_sgtable API comments from arm to common code
Date: Thu,  8 Aug 2019 18:59:59 +0300
Message-ID: <20190808160005.10325-3-hch@lst.de> (raw)
In-Reply-To: <20190808160005.10325-1-hch@lst.de>

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

Signed-off-by: Christoph Hellwig <hch@lst.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 ad64d32fb39a..b4d65da76393 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -880,17 +880,6 @@ 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 9c0f6a8eb5cb..41590d003465 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


  parent reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-08 15:59 remove default fallbacks in dma_map_ops v3 Christoph Hellwig
2019-08-08 15:59 ` [PATCH 1/8] dma-mapping: provide a better default ->get_required_mask Christoph Hellwig
2019-08-08 15:59 ` Christoph Hellwig [this message]
2019-08-08 16:00 ` [PATCH 3/8] dma-mapping: explicitly wire up ->mmap and ->get_sgtable Christoph Hellwig
2019-08-08 16:00 ` [PATCH 4/8] dma-mapping: add a dma_can_mmap helper Christoph Hellwig
2019-08-08 16:00 ` [PATCH 5/8] ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap_* Christoph Hellwig
2019-08-08 16:00 ` [PATCH 6/8] arm-nommu: call dma_mmap_from_dev_coherent directly Christoph Hellwig
2019-08-09  9:35   ` Sergei Shtylyov
2019-08-08 16:00 ` [PATCH 7/8] parisc: don't set ARCH_NO_COHERENT_DMA_MMAP Christoph Hellwig
2019-08-15  7:36   ` Christoph Hellwig
2019-08-15  9:25   ` James Bottomley
2019-08-15 10:50     ` Christoph Hellwig
2019-08-19 14:25       ` Christoph Hellwig
2019-08-08 16:00 ` [PATCH 8/8] dma-mapping: remove CONFIG_ARCH_NO_COHERENT_DMA_MMAP Christoph Hellwig
2019-08-09  7:21   ` Geert Uytterhoeven
2019-08-29 15:38 ` remove default fallbacks in dma_map_ops v3 Christoph Hellwig

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