Commit eba304c6 authored by Christoph Hellwig's avatar Christoph Hellwig

dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR

Move the comment documenting dma_addr_t away from the dma_map_ops
definition which isn't very related to it, and toward DMA_MAPPING_ERROR,
which is somewhat related.  Add a little blurb about DMA_MAPPING_ERROR
as well.
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
parent db4268f8
......@@ -67,12 +67,6 @@
*/
#define DMA_ATTR_PRIVILEGED (1UL << 9)
/*
* A dma_addr_t can hold any valid DMA or bus address for the platform.
* It can be given to a device to use as a DMA source or target. A CPU cannot
* reference a dma_addr_t directly because there may be translation between
* its physical address space and the bus address space.
*/
struct dma_map_ops {
void* (*alloc)(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t gfp,
......@@ -131,6 +125,16 @@ struct dma_map_ops {
unsigned long (*get_merge_boundary)(struct device *dev);
};
/*
* A dma_addr_t can hold any valid DMA or bus address for the platform. It can
* be given to a device to use as a DMA source or target. It is specific to a
* given device and there may be a translation between the CPU physical address
* space and the bus address space.
*
* DMA_MAPPING_ERROR is the magic error code if a mapping failed. It should not
* be used directly in drivers, but checked for using dma_mapping_error()
* instead.
*/
#define DMA_MAPPING_ERROR (~(dma_addr_t)0)
extern const struct dma_map_ops dma_virt_ops;
......
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