powerpc: Fix circular dependency between percpu.h and mmu.h

[linux-2.6-microblaze.git] / Documentation / memory-barriers.txt

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index eaabc31..ff07cd3 100644 (file)
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1935,6 +1935,20 @@ There are some more advanced barrier functions:
      relaxed I/O accessors and the Documentation/DMA-API.txt file for more
      information on consistent memory.
 
+ (*) pmem_wmb();
+
+     This is for use with persistent memory to ensure that stores for which
+     modifications are written to persistent storage reached a platform
+     durability domain.
+
+     For example, after a non-temporal write to pmem region, we use pmem_wmb()
+     to ensure that stores have reached a platform durability domain. This ensures
+     that stores have updated persistent storage before any data access or
+     data transfer caused by subsequent instructions is initiated. This is
+     in addition to the ordering done by wmb().
+
+     For load from persistent memory, existing read memory barriers are sufficient
+     to ensure read ordering.
 
 ===============================
 IMPLICIT KERNEL MEMORY BARRIERS