Add the atomic_thread_fence() family of functions with intent to

provide a semantic defined by the C11 fences with corresponding
memory_order.

atomic_thread_fence_acq() gives r | r, w, where r and w are read and
write accesses, and | denotes the fence itself.

atomic_thread_fence_rel() is r, w | w.

atomic_thread_fence_acq_rel() is the combination of the acquire and
release in single operation.  Note that reads after the acq+rel fence
could be made visible before writes preceeding the fence.

atomic_thread_fence_seq_cst() orders all accesses before/after the
fence, and the fence itself is globally ordered against other
sequentially consistent atomic operations.

Reviewed by:	alc
Discussed with:	bde
Sponsored by:	The FreeBSD Foundation
MFC after:	3 weeks

1 files changed, 28 insertions, 0 deletions

diff --git a/sys/mips/include/atomic.h b/sys/mips/include/atomic.h
index b43cc61..d4b951e 100644
--- a/sys/mips/include/atomic.h
+++ b/sys/mips/include/atomic.h
@@ -496,6 +496,34 @@ atomic_fetchadd_64(__volatile uint64_t *p, uint64_t v)
 }
 #endif
 
+static __inline void
+atomic_thread_fence_acq(void)
+{
+
+	mips_sync();
+}
+
+static __inline void
+atomic_thread_fence_rel(void)
+{
+
+	mips_sync();
+}
+
+static __inline void
+atomic_thread_fence_acq_rel(void)
+{
+
+	mips_sync();
+}
+
+static __inline void
+atomic_thread_fence_seq_cst(void)
+{
+
+	mips_sync();
+}
+
 /* Operations on chars. */
 #define	atomic_set_char		atomic_set_8
 #define	atomic_set_acq_char	atomic_set_acq_8