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dma: document dma_*map*_attrs() interfaces

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Document the new dma_*map*_attrs() functions.

[[email protected]: fix up for dma-add-dma_map_attrs-interfaces and update docs]
Signed-off-by: Arthur Kepner <[email protected]>
Acked-by: David S. Miller <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Jesse Barnes <[email protected]>
Cc: Jes Sorensen <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Roland Dreier <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Grant Grundler <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: Mark Nelson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Arthur Kepner 2008-04-29 01:00:31 -07:00 • committed by Linus Torvalds
commit a75b0a2f68
2 changed files with 89 additions and 0 deletions
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65
Documentation/DMA-API.txt
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@ -395,6 +395,71 @@ Notes: You must do this:
See also dma_map_single().
dma_addr_t
dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
enum dma_data_direction dir,
struct dma_attrs *attrs)
void
dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr,
size_t size, enum dma_data_direction dir,
struct dma_attrs *attrs)
int
dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
int nents, enum dma_data_direction dir,
struct dma_attrs *attrs)
void
dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl,
int nents, enum dma_data_direction dir,
struct dma_attrs *attrs)
The four functions above are just like the counterpart functions
without the _attrs suffixes, except that they pass an optional
struct dma_attrs*.
struct dma_attrs encapsulates a set of "dma attributes". For the
definition of struct dma_attrs see linux/dma-attrs.h.
The interpretation of dma attributes is architecture-specific, and
each attribute should be documented in Documentation/DMA-attributes.txt.
If struct dma_attrs* is NULL, the semantics of each of these
functions is identical to those of the corresponding function
without the _attrs suffix. As a result dma_map_single_attrs()
can generally replace dma_map_single(), etc.
As an example of the use of the *_attrs functions, here's how
you could pass an attribute DMA_ATTR_FOO when mapping memory
for DMA:
#include <linux/dma-attrs.h>
/* DMA_ATTR_FOO should be defined in linux/dma-attrs.h and
* documented in Documentation/DMA-attributes.txt */
...
DEFINE_DMA_ATTRS(attrs);
dma_set_attr(DMA_ATTR_FOO, &attrs);
....
n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, &attr);
....
Architectures that care about DMA_ATTR_FOO would check for its
presence in their implementations of the mapping and unmapping
routines, e.g.:
void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
size_t size, enum dma_data_direction dir,
struct dma_attrs *attrs)
{
....
int foo = dma_get_attr(DMA_ATTR_FOO, attrs);
....
if (foo)
/* twizzle the frobnozzle */
....
Part II - Advanced dma_ usage
-----------------------------