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.
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
Documentation/memory-barriers.txt | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index b12df9137e1c..1eabcc0e4eca 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1894,10 +1894,13 @@ 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
- DMA capable device.
+ DMA capable device, in the case of ensure the prior (both reads and
+ writes) accesses to memory by a CPU are ordered w.r.t. a subsequent
+ MMIO write, dma_mb().
For example, consider a device driver that shares memory with a device
and uses a descriptor status value to indicate if the descriptor belongs
--
2.35.3
