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-rw-r--r--Documentation/memory-barriers.txt19
1 files changed, 10 insertions, 9 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 6dafc8085acc..a02d6bbfc9d0 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1920,9 +1920,6 @@ There are some more advanced barrier functions:
/* assign ownership */
desc->status = DEVICE_OWN;
- /* force memory to sync before notifying device via MMIO */
- wmb();
-
/* notify device of new descriptors */
writel(DESC_NOTIFY, doorbell);
}
@@ -1930,11 +1927,15 @@ There are some more advanced barrier functions:
The dma_rmb() allows us guarantee the device has released ownership
before we read the data from the descriptor, and the dma_wmb() allows
us to guarantee the data is written to the descriptor before the device
- can see it now has ownership. The wmb() is needed to guarantee that the
- cache coherent memory writes have completed before attempting a write to
- the cache incoherent MMIO region.
+ can see it now has ownership. Note that, when using writel(), a prior
+ wmb() is not needed to guarantee that the cache coherent memory writes
+ have completed before writing to the MMIO region. The cheaper
+ writel_relaxed() does not provide this guarantee and must not be used
+ here.
- See Documentation/DMA-API.txt for more information on consistent memory.
+ See the subsection "Kernel I/O barrier effects" for more information on
+ relaxed I/O accessors and the Documentation/DMA-API.txt file for more
+ information on consistent memory.
MMIO WRITE BARRIER
@@ -2903,7 +2904,7 @@ is discarded from the CPU's cache and reloaded. To deal with this, the
appropriate part of the kernel must invalidate the overlapping bits of the
cache on each CPU.
-See Documentation/cachetlb.txt for more information on cache management.
+See Documentation/core-api/cachetlb.rst for more information on cache management.
CACHE COHERENCY VS MMIO
@@ -3083,7 +3084,7 @@ CIRCULAR BUFFERS
Memory barriers can be used to implement circular buffering without the need
of a lock to serialise the producer with the consumer. See:
- Documentation/circular-buffers.txt
+ Documentation/core-api/circular-buffers.rst
for details.