[PATCH] drm/i915/active: Use try_cmpxchg() in active_fence_cb()

[Uros Bizjak]

Replace this pattern in active_fence_cb():

    cmpxchg(*ptr, old, new) == old

... with the simpler and faster:

    try_cmpxchg(*ptr, &old, new)

The x86 CMPXCHG instruction returns success in the ZF flag,
so this change saves a compare after the CMPXCHG.

Signed-off-by: Uros Bizjak <ubiz...@gmail.com>
Cc: Jani Nikula <jani.nik...@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.v...@intel.com>
Cc: Tvrtko Ursulin <tursu...@ursulin.net>
Cc: David Airlie <airl...@gmail.com>
Cc: Simona Vetter <sim...@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_active.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_active.c 
b/drivers/gpu/drm/i915/i915_active.c
index 5ec293011d99..35319228bc51 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -212,7 +212,7 @@ active_fence_cb(struct dma_fence *fence, struct 
dma_fence_cb *cb)
        struct i915_active_fence *active =
                container_of(cb, typeof(*active), cb);
 
-       return cmpxchg(__active_fence_slot(active), fence, NULL) == fence;
+       return try_cmpxchg(__active_fence_slot(active), &fence, NULL);
 }
 
 static void
-- 
2.46.2