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| -rw-r--r-- | Documentation/memory-barriers.txt | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 22a969cdd476..4af4cea8cff0 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -2465,10 +2465,15 @@ 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() |