summaryrefslogtreecommitdiff
path: root/Documentation/DMA-attributes.txt
diff options
context:
space:
mode:
authorArthur Kepner <akepner@sgi.com>2008-04-29 01:00:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-29 08:06:11 -0700
commita75b0a2f68d3937f96ed39525e4750601483e3b4 (patch)
tree1a84f2ef16515880f00e2db9a931299f22a07071 /Documentation/DMA-attributes.txt
parent74bc7ceebfa1c84ddd3a843ebfb56df013bf7ef5 (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.txt24
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.
+