[Intel-gfx] [PATCH 2/6] drm/i915: Skip taking acquire mutex for no ref->active callback

[Chris Wilson]

If no active callback is defined for i915_active, we do not need to
serialise its enabling with the mutex. We still do only want to call the
debug activate once, and must still serialise with a concurrent retire.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_active.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index d960d0be5bd2..841b5c30950a 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -416,6 +416,14 @@ bool i915_active_acquire_if_busy(struct i915_active *ref)
 	return atomic_add_unless(&ref->count, 1, 0);
 }
 
+static void __i915_active_activate(struct i915_active *ref)
+{
+	spin_lock_irq(&ref->tree_lock); /* __active_retire() */
+	if (!atomic_fetch_inc(&ref->count))
+		debug_active_activate(ref);
+	spin_unlock_irq(&ref->tree_lock);
+}
+
 int i915_active_acquire(struct i915_active *ref)
 {
 	int err;
@@ -423,23 +431,22 @@ int i915_active_acquire(struct i915_active *ref)
 	if (i915_active_acquire_if_busy(ref))
 		return 0;
 
+	if (!ref->active) {
+		__i915_active_activate(ref);
+		return 0;
+	}
+
 	err = mutex_lock_interruptible(&ref->mutex);
 	if (err)
 		return err;
 
 	if (likely(!i915_active_acquire_if_busy(ref))) {
-		if (ref->active)
-			err = ref->active(ref);
-		if (!err) {
-			spin_lock_irq(&ref->tree_lock); /* __active_retire() */
-			debug_active_activate(ref);
-			atomic_inc(&ref->count);
-			spin_unlock_irq(&ref->tree_lock);
-		}
+		err = ref->active(ref);
+		if (!err)
+			__i915_active_activate(ref);
 	}
 
 	mutex_unlock(&ref->mutex);
-
 	return err;
 }
 
-- 
2.20.1