Messages in this thread Patch in this message | | | From | Parav Pandit <> | Subject | [PATCH] locking/memory-barriers.txt: Improve documentation for writel() usage | Date | Thu, 15 Sep 2022 08:01:06 +0300 |
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The cited commit [1] describes that when using writel(), explcit wmb() is not needed. However, it should have said that dma_wmb() is not needed.
Hence update the example to be more accurate that matches the current implementation and document section of dma_wmb()/dma_rmb().
[1] commit 5846581e3563 ("locking/memory-barriers.txt: Fix broken DMA vs. MMIO ordering example") Signed-off-by: Parav Pandit <parav@nvidia.com> --- Documentation/memory-barriers.txt | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 832b5d36e279..cc3a15ac53b3 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1927,10 +1927,10 @@ There are some more advanced barrier functions: 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 dma_mb() implies both a dma_rmb() and - a dma_wmb(). 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. + a dma_wmb(). Note that, when using writel(), a prior dma_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 the subsection "Kernel I/O barrier effects" for more information on relaxed I/O accessors and the Documentation/core-api/dma-api.rst file for -- 2.26.2
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