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Subject[PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR
Date
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: Christoph Hellwig <hch@lst.de>
---
include/linux/dma-mapping.h | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 51e93d44b826c8..c4395cf7e265dd 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -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. A CPU cannot
+ * reference a dma_addr_t directly because there may be translation between its
+ * 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;
--
2.28.0
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