Will Deacon proposed the RELEASE/ACQUIRE/RELAXED semantics for atomic operations(https://lkml.org/lkml/2015/8/6/498), which has been already merged in 4.3-rc1. More people tend to use it for better performance(https://lkml.org/lkml/2015/9/20/47). These semantics are proposed for better fitting the need of high scalability.
However, the efficient implementation hasn't been merged yet. As we have a weaker memory order model on POWER, if we didn't implement these atomics efficently, there would be no benefit we can gain from these new operations.
A proposal of an efficient implemenation has been sent out to upstream(https://lkml.org/lkml/2015/9/16/527), hopefully will get merged. Still there may be more atomics having RELEASE and ACQUIRE semantics, and there need more effort to implement them correctly. Also, we need to spread these new atomic variants to LTC kernel team to understand what they can provide and how to use them.
> Was this feature already accepted upstream?
Not yet, still waiting to get into the maintainer's tree, but there is no obvious objection to this feature.
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