diff options
| author | Arthur Kepner <akepner@sgi.com> | 2008-04-29 01:00:31 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-04-29 08:06:11 -0700 |
| commit | a75b0a2f68d3937f96ed39525e4750601483e3b4 (patch) | |
| tree | 1a84f2ef16515880f00e2db9a931299f22a07071 /Documentation/DMA-attributes.txt | |
| parent | 74bc7ceebfa1c84ddd3a843ebfb56df013bf7ef5 (diff) | |
dma: document dma_*map*_attrs() interfaces
Document the new dma_*map*_attrs() functions.
[markn@au1.ibm.com: fix up for dma-add-dma_map_attrs-interfaces and update docs]
Signed-off-by: Arthur Kepner <akepner@sgi.com>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Roland Dreier <rdreier@cisco.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Grant Grundler <grundler@parisc-linux.org>
Cc: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Mark Nelson <markn@au1.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/DMA-attributes.txt')
| -rw-r--r-- | Documentation/DMA-attributes.txt | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt new file mode 100644 index 000000000000..6d772f84b477 --- /dev/null +++ b/Documentation/DMA-attributes.txt @@ -0,0 +1,24 @@ + DMA attributes + ============== + +This document describes the semantics of the DMA attributes that are +defined in linux/dma-attrs.h. + +DMA_ATTR_WRITE_BARRIER +---------------------- + +DMA_ATTR_WRITE_BARRIER is a (write) barrier attribute for DMA. DMA +to a memory region with the DMA_ATTR_WRITE_BARRIER attribute forces +all pending DMA writes to complete, and thus provides a mechanism to +strictly order DMA from a device across all intervening busses and +bridges. This barrier is not specific to a particular type of +interconnect, it applies to the system as a whole, and so its +implementation must account for the idiosyncracies of the system all +the way from the DMA device to memory. + +As an example of a situation where DMA_ATTR_WRITE_BARRIER would be +useful, suppose that a device does a DMA write to indicate that data is +ready and available in memory. The DMA of the "completion indication" +could race with data DMA. Mapping the memory used for completion +indications with DMA_ATTR_WRITE_BARRIER would prevent the race. + |