On Tue, Dec 21, 2021 at 4:55 AM Xiongfeng Wang
[off-list ref] wrote:

For memory accesses with write-combining attributes (e.g. those returned
by ioremap_wc()), the CPU may wait for prior accesses to be merged with
subsequent ones. But in some situation, such wait is bad for the
performance.

We introduce io_stop_wc() to prevent the merging of write-combining
memory accesses before this macro with those after it.

We add implementation for ARM64 using DGH instruction and provide NOP
implementation for other architectures.

Signed-off-by: Xiongfeng Wang <redacted>
Suggested-by: Will Deacon <will@kernel.org>
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
---
v1->v2: change 'Normal-Non Cacheable' to 'write-combining'

For asm-generic:

Acked-by: Arnd Bergmann <arnd@arndb.de>

Will, Catalin: if you are happy with this version, please merge it through the
arm64 tree.