Signed-off-by: Richard Henderson <r...@twiddle.net>
---
arch/alpha/Kconfig | 1 +
arch/alpha/include/asm/atomic.h | 28 ++++++++++++++++++++++++++++
2 files changed, 29 insertions(+)
diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 837a1f2..082d9b4 100644
--- 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
--- 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)
--
1.8.1.4
--
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