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.
Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx> # for asm-generic
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..832b5d36e279 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.
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
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index fd7e8fbaeef1..961f4d88f9ef 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -38,6 +38,10 @@
#define wmb() do { kcsan_wmb(); __wmb(); } while (0)
#endif
+#ifdef __dma_mb
+#define dma_mb() do { kcsan_mb(); __dma_mb(); } while (0)
+#endif
+
#ifdef __dma_rmb
#define dma_rmb() do { kcsan_rmb(); __dma_rmb(); } while (0)
#endif
@@ -65,6 +69,10 @@
#define wmb() mb()
#endif
+#ifndef dma_mb
+#define dma_mb() mb()
+#endif
+
#ifndef dma_rmb
#define dma_rmb() rmb()
#endif
--
2.35.3
