Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[firefly-linux-kernel-4.4.55.git] / Documentation / memory-barriers.txt

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index f7fa63508abaca685d5c235298047cab3fabbc74..7ee2ae6d5451d120126a04e3deeb07c02f2f9671 100644 (file)
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -2483,10 +2483,15 @@ functions:
      Please refer to the PCI specification for more information on interactions
      between PCI transactions.
 
- (*) readX_relaxed()
-
-     These are similar to readX(), but are not guaranteed to be ordered in any
-     way. Be aware that there is no I/O read barrier available.
+ (*) readX_relaxed(), writeX_relaxed()
+
+     These are similar to readX() and writeX(), but provide weaker memory
+     ordering guarantees. Specifically, they do not guarantee ordering with
+     respect to normal memory accesses (e.g. DMA buffers) nor do they guarantee
+     ordering with respect to LOCK or UNLOCK operations. If the latter is
+     required, an mmiowb() barrier can be used. Note that relaxed accesses to
+     the same peripheral are guaranteed to be ordered with respect to each
+     other.
 
  (*) ioreadX(), iowriteX()