[RFC v2 3/7] powerpc: atomic: Implement atomic{,64}_{add,sub}_return_* variants

[Will Deacon]

On Wed, Sep 16, 2015 at 04:49:31PM +0100, Boqun Feng wrote:
> On powerpc, we don't need a general memory barrier to achieve acquire and
> release semantics, so __atomic_op_{acquire,release} can be implemented
> using "lwsync" and "isync".

I'm assuming isync+ctrl isn't transitive, so we need to get to the bottom
of the s390 thread you linked me to before we start spreading this
further:

  https://lkml.org/lkml/2015/9/15/836

Will