Commit 14451467 authored Mar 15, 2019 by Christoph Hellwig

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@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)