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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>
This commit is contained in:
Christoph Hellwig 2019-03-15 17:56:43 +01:00
parent 392e879a44
commit 1445146701
2 changed files with 11 additions and 11 deletions
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11
arch/arm/mm/dma-mapping.c
View File

@ -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)

11
kernel/dma/mapping.c
View File

@ -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)