tile: support atomic64_dec_if_positive()

Use the normal cmpxchg() idiom to implement this functionality.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

2 files changed, 22 insertions, 0 deletions

diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
index 0e500d90c2a0..9a9d08637ab9 100644
--- a/arch/tile/Kconfig
+++ b/arch/tile/Kconfig
@@ -24,6 +24,7 @@ config TILE
         select MODULES_USE_ELF_RELA
         select HAVE_ARCH_TRACEHOOK
         select HAVE_SYSCALL_TRACEPOINTS
+        select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 
 # FIXME: investigate whether we need/want these options.
 #       select HAVE_IOREMAP_PROT
diff --git a/arch/tile/include/asm/atomic.h b/arch/tile/include/asm/atomic.h
index f2461429a4a4..e71387ab20ca 100644
--- a/arch/tile/include/asm/atomic.h
+++ b/arch/tile/include/asm/atomic.h
@@ -131,4 +131,25 @@ static inline int atomic_read(const atomic_t *v)
 #include <asm/atomic_64.h>
 #endif
 
+#ifndef __ASSEMBLY__
+
+static inline long long atomic64_dec_if_positive(atomic64_t *v)
+{
+        long long c, old, dec;
+
+        c = atomic64_read(v);
+        for (;;) {
+                dec = c - 1;
+                if (unlikely(dec < 0))
+                        break;
+                old = atomic64_cmpxchg((v), c, dec);
+                if (likely(old == c))
+                        break;
+                c = old;
+        }
+        return dec;
+}
+
+#endif /* __ASSEMBLY__ */
+
 #endif /* _ASM_TILE_ATOMIC_H */