On 2022/5/23 16:22, Marco Elver wrote:
On Mon, 23 May 2022 at 03:50, Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:The memory barrier dma_mb() is introduced by commit a76a37777f2c ("iommu/arm-smmu-v3: Ensure queue is read after updating prod pointer"), which is used to ensure that prior (both reads and writes) accesses to memory by a CPU are ordered w.r.t. a subsequent MMIO write, this is only defined on arm64, but it is a generic memory barrier, let's add dma_mb() into documentation and include/asm-generic/barrier.h. Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> --- Documentation/memory-barriers.txt | 11 ++++++----- include/asm-generic/barrier.h | 8 ++++++++ 2 files changed, 14 insertions(+), 5 deletions(-) diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index b12df9137e1c..07a8b8e1b12a 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1894,6 +1894,7 @@ There are some more advanced barrier functions: (*) dma_wmb(); (*) dma_rmb(); + (*) dma_mb(); These are for use with consistent memory to guarantee the ordering of writes or reads of shared memory accessible to both the CPU and a @@ -1925,11 +1926,11 @@ 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. 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. + 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.It seems you've changed that spacing. This document uses 2 spaces after a sentence-ending '.'. (My original suggestion included the 2 spaces after dots.)
I don't know the rules, it seems that some uses 1 spaces, others are 2 spaces, but most
uses 2 spaces, will update.
Otherwise it all looks fine to me. Thanks, -- Marco .
