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Commit 14451467 authored by Christoph Hellwig's avatar Christoph Hellwig
Browse files

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: default avatarChristoph Hellwig <hch@lst.de>
parent 392e879a

arch/arm/mm/dma-mapping.c

+0 −11
Original line number Diff line number Diff line
@@ -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)

kernel/dma/mapping.c

+11 −0
Original line number Diff line number Diff line
@@ -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)