[dpdk-dev] [PATCH v2 1/3] eal/arm64: relax the io barrier for aarch64

[Gavin Hu]

Armv8's peripheral coherence order is a total order on all reads and writes
to that peripheral.[1]

The peripheral coherence order for a memory-mapped peripheral signifies the
order in which accesses arrive at the endpoint.  For a read or a write RW1
and a read or a write RW2 to the same peripheral, then RW1 will appear in
the peripheral coherence order for the peripheral before RW2 if either of
the following cases apply:
 1. RW1 and RW2 are accesses using Non-cacheable or Device attributes and
    RW1 is Ordered-before RW2.
 2. RW1 and RW2 are accesses using Device-nGnRE or Device-nGnRnE attributes
    and RW1 appears in program order before RW2.

On arm platforms, all the PCI resources are mapped to nGnRE device memory
[2], the above case 2 holds true, that means the peripheral coherence order
applies here and just a compiler barrier is sufficient for rte io barriers.

[1] Section B2.3.4 of ARMARM, https://developer.arm.com/docs/ddi0487/lates
t/arm-architecture-reference-manual-armv8-for-armv8-a-architecture-profile
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
tree/drivers/pci/pci-sysfs.c#n1204

Signed-off-by: Gavin Hu <gavin.hu at arm.com>
Reviewed-by: Steve Capper <steve.capper at arm.com>
Reviewed-by: Phil Yang <phil.yang at arm.com>
---
 lib/librte_eal/common/include/arch/arm/rte_atomic_64.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
index 859ae12..fd63956 100644
--- a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
+++ b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
@@ -34,11 +34,11 @@ extern "C" {
 
 #define rte_smp_rmb() dmb(ishld)
 
-#define rte_io_mb() rte_mb()
+#define rte_io_mb() rte_compiler_barrier()
 
-#define rte_io_wmb() rte_wmb()
+#define rte_io_wmb() rte_compiler_barrier()
 
-#define rte_io_rmb() rte_rmb()
+#define rte_io_rmb() rte_compiler_barrier()
 
 #define rte_cio_wmb() dmb(oshst)
 
-- 
2.7.4