[lkml]   [2007]   [Oct]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 3/5] dma: document dma_flags_set_attr()

Document dma_flags_set_attr().

Signed-off-by: Arthur Kepner <>


DMA-API.txt | 27 +++++++++++++++++++++++++++
1 files changed, 27 insertions(+)

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index cc7a8c3..16e15c0 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -544,3 +544,30 @@ size is the size (and should be a page-sized multiple).
The return value will be either a pointer to the processor virtual
address of the memory, or an error (via PTR_ERR()) if any part of the
region is occupied.
+dma_flags_set_attr(u32 attr, enum dma_data_direction dir)
+Amend dir with a platform-specific "dma attribute".
+The only attribute currently defined is DMA_BARRIER_ATTR, which causes
+in-flight DMA to be flushed when the associated memory region is written
+to (see example below). Setting DMA_BARRIER_ATTR provides a mechanism
+to enforce ordering of DMA on platforms that permit DMA to be reordered
+between device and host memory (within a NUMA interconnect). On other
+platforms this is a nop.
+DMA_BARRIER_ATTR would be set when the memory region is mapped for DMA,
+ int count;
+ int flags = dma_flags_set_attr(DMA_BARRIER_ATTR, DMA_BIDIRECTIONAL);
+ ....
+ count = dma_map_sg(dev, sglist, nents, flags);
+As an example of a situation where this would be useful, suppose that
+the 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. Using DMA_BARRIER_ATTR on the memory used for
+completion indications would prevent the race.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at
 \ /
  Last update: 2007-10-03 04:51    [W:0.029 / U:8.652 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site