dma-mapping: remove the DMA_ATTR_WRITE_BARRIER flag

[tomoyo/tomoyo-test1.git] / Documentation / DMA-attributes.txt

diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index 8f8d97f..29dcbe8 100644 (file)
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -5,24 +5,6 @@ DMA attributes
 This document describes the semantics of the DMA attributes that are
 defined in linux/dma-mapping.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 idiosyncrasies 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.
-
 DMA_ATTR_WEAK_ORDERING
 ----------------------