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Subject[PATCH 1.5/5] alpha: atomic: provide asm for the fastpath for _atomic_dec_and_lock_irqsave
I just looked at Alpha's atomic_dec_and_lock assembly and did something
that should work for atomic_dec_and_lock_irqsave. I think it works but I
would prefer for someone from the Alpha-Camp to ack this before it goes
in. It is not critical because the non-optimized version should work.

Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: linux-alpha@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/alpha/lib/dec_and_lock.c | 33 ++++++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/arch/alpha/lib/dec_and_lock.c b/arch/alpha/lib/dec_and_lock.c
index 069fef7372dc..d29ba1de4f68 100644
--- a/arch/alpha/lib/dec_and_lock.c
+++ b/arch/alpha/lib/dec_and_lock.c
@@ -32,6 +32,28 @@ _atomic_dec_and_lock: \n\
.previous \n\
.end _atomic_dec_and_lock");

+ asm (".text \n\
+ .global _atomic_dec_and_lock_irqsave \n\
+ .ent _atomic_dec_and_lock_irqsave \n\
+ .align 4 \n\
+_atomic_dec_and_lock_irqsave: \n\
+ .prologue 0 \n\
+1: ldl_l $1, 0($16) \n\
+ subl $1, 1, $1 \n\
+ beq $1, 2f \n\
+ stl_c $1, 0($16) \n\
+ beq $1, 4f \n\
+ mb \n\
+ clr $0 \n\
+ ret \n\
+2: br $29, 3f \n\
+3: ldgp $29, 0($29) \n\
+ br $atomic_dec_and_lock_irqsave1..ng \n\
+ .subsection 2 \n\
+4: br 1b \n\
+ .previous \n\
+ .end _atomic_dec_and_lock_irqsave");
+
static int __used atomic_dec_and_lock_1(atomic_t *atomic, spinlock_t *lock)
{
/* Slow path */
@@ -43,14 +65,11 @@ static int __used atomic_dec_and_lock_1(atomic_t *atomic, spinlock_t *lock)
}
EXPORT_SYMBOL(_atomic_dec_and_lock);

-int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
- unsigned long *flags)
+static int __used atomic_dec_and_lock_irqsave1(atomic_t *atomic,
+ spinlock_t *lock,
+ unsigned long *flags)
{
- /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
- if (atomic_add_unless(atomic, -1, 1))
- return 0;
-
- /* Otherwise do it the slow way */
+ /* Slow way */
spin_lock_irqsave(lock, *flags);
if (atomic_dec_and_test(atomic))
return 1;
--
2.17.1
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