[PATCH v2] arm64: barrier: implement wfe-based smp_cond_load_acquire

[peterz@infradead.org (Peter Zijlstra)]

On Thu, Jun 30, 2016 at 02:00:17PM +0100, Will Deacon wrote:
> On Mon, Jun 27, 2016 at 06:43:54PM +0100, Will Deacon wrote:
> > smp_cond_load_acquire is used to spin on a variable until some
> > expression involving that variable becomes true.
> > 
> > On arm64, we can build this using WFE and LDXR, since clearing of the
> > exclusive monitor as a result of the variable being changed by another
> > CPU generates an event, which will wake us up out of WFE.
> > 
> > This patch implements smp_cond_load_acquire using LDXR and WFE, which
> > themselves are contained in an internal __cmpwait function.
> > 
> > Signed-off-by: Will Deacon <will.deacon@arm.com>
> > ---
> > 
> > Based on Peter's locking/core branch.
> > 
> > v1->v2: Use cmpwait_relaxed
> > 
> >  arch/arm64/include/asm/barrier.h | 13 ++++++++++
> >  arch/arm64/include/asm/cmpxchg.h | 51 ++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 64 insertions(+)
> 
> Peter -- could you take this one via locking/core for 4.8, please? I don't
> anticipate any conflicts with the arm64 tree and it relies on your other
> cond-wait patches anyway.

OK, queued it. Thanks!