alpha: Implement atomic64_dec_if_positive

Reviewed-and-Tested-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 837a1f2..082d9b4 100644 (file)
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -15,6 +15,7 @@ config ALPHA
        select ARCH_WANT_OPTIONAL_GPIOLIB
        select ARCH_WANT_IPC_PARSE_VERSION
        select ARCH_HAVE_NMI_SAFE_CMPXCHG
+       select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
        select GENERIC_SMP_IDLE_THREAD
        select GENERIC_CMOS_UPDATE
        select GENERIC_STRNCPY_FROM_USER

diff --git a/arch/alpha/include/asm/atomic.h b/arch/alpha/include/asm/atomic.h
index 0dc18fc..78b03ef 100644 (file)
--- a/arch/alpha/include/asm/atomic.h
+++ b/arch/alpha/include/asm/atomic.h
@@ -238,6 +238,34 @@ static __inline__ int atomic64_add_unless(atomic64_t *v, long a, long u)
        return !c;
 }
 
+/*
+ * atomic64_dec_if_positive - decrement by 1 if old value positive
+ * @v: pointer of type atomic_t
+ *
+ * The function returns the old value of *v minus 1, even if
+ * the atomic variable, v, was not decremented.
+ */
+static inline long atomic64_dec_if_positive(atomic64_t *v)
+{
+       long old, tmp;
+       smp_mb();
+       __asm__ __volatile__(
+       "1:     ldq_l   %[old],%[mem]\n"
+       "       subq    %[old],1,%[tmp]\n"
+       "       ble     %[old],2f\n"
+       "       stq_c   %[tmp],%[mem]\n"
+       "       beq     %[tmp],3f\n"
+       "2:\n"
+       ".subsection 2\n"
+       "3:     br      1b\n"
+       ".previous"
+       : [old] "=&r"(old), [tmp] "=&r"(tmp)
+       : [mem] "m"(*v)
+       : "memory");
+       smp_mb();
+       return old - 1;
+}
+
 #define atomic64_inc_not_zero(v) atomic64_add_unless((v), 1, 0)
 
 #define atomic_add_negative(a, v) (atomic_add_return((a), (v)) < 0)