Re: [RFC 3/5] powerpc: atomic: implement atomic{,64}_{add,sub}_return_* variants

[Boqun Feng]

Hi Peter,

On Fri, Aug 28, 2015 at 12:48:54PM +0200, Peter Zijlstra wrote:
> On Fri, Aug 28, 2015 at 10:48:17AM +0800, Boqun Feng wrote:
> > +/*
> > + * Since {add,sub}_return_relaxed and xchg_relaxed are implemented with
> > + * a "bne-" instruction at the end, so an isync is enough as a acquire 
> > barrier
> > + * on the platform without lwsync.
> > + */
> > +#ifdef CONFIG_SMP
> > +#define smp_acquire_barrier__after_atomic() \
> > +   __asm__ __volatile__(PPC_ACQUIRE_BARRIER : : : "memory")
> > +#else
> > +#define smp_acquire_barrier__after_atomic() barrier()
> > +#endif
> > +#define arch_atomic_op_acquire(op, args...)                                
> > \
> > +({                                                                 \
> > +   typeof(op##_relaxed(args)) __ret  = op##_relaxed(args);         \
> > +   smp_acquire_barrier__after_atomic();                            \
> > +   __ret;                                                          \
> > +})
> > +
> > +#define arch_atomic_op_release(op, args...)                                
> > \
> > +({                                                                 \
> > +   smp_lwsync();                                                   \
> > +   op##_relaxed(args);                                             \
> > +})
> 
> Urgh, so this is RCpc. We were trying to get rid of that if possible.
> Lets wait until that's settled before introducing more of it.
> 
> lkml.kernel.org/r/20150820155604.gb24...@arm.com

OK, get it. Thanks.

So I'm not going to introduce these arch specific macros, I think what I
need to implement are just _relaxed variants and cmpxchg_acquire.

Regards,
Boqun

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