On Fri, Aug 28, 2015 at 10:48:16AM +0800, Boqun Feng wrote:
> Some architectures may have their special barriers for acquire, release
> and fence semantics, general memory barriers(smp_mb__*_atomic()) in
> __atomic_op_*() may be too strong, so arch_atomic_op_*() helpers are
> introduced for architectures to provide their own version helpers to
> build different variants based on _relaxed variants.
>
> Signed-off-by: Boqun Feng <boqun.f...@gmail.com>
> ---
> include/linux/atomic.h | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/include/linux/atomic.h b/include/linux/atomic.h
> index 00a5763..622255b 100644
> --- a/include/linux/atomic.h
> +++ b/include/linux/atomic.h
> @@ -34,20 +34,33 @@
> * The idea here is to build acquire/release variants by adding explicit
> * barriers on top of the relaxed variant. In the case where the relaxed
> * variant is already fully ordered, no additional barriers are needed.
> + *
> + * Besides, if an arch has a special barrier for acquire/release, it could
> + * implement its own arch_atomic_op_* and use the same framework for building
> + * variants
> */
> +#ifndef arch_atomic_op_acquire
> #define __atomic_op_acquire(op, args...) \
> ({ \
> typeof(op##_relaxed(args)) __ret = op##_relaxed(args); \
> smp_mb__after_atomic(); \
> __ret; \
> })
> +#else
> +#define __atomic_op_acquire arch_atomic_op_acquire
> +#endif
Not really a fan of this, its not consistent with the existing #ifndef
guard style.
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