[Intel-gfx] [PATCH 02/21] 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 <ch...@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellst...@intel.com>
---
 drivers/gpu/drm/i915/i915_active.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_active.c 
b/drivers/gpu/drm/i915/i915_active.c
index d960d0be5bd2..500537889e66 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;
@@ -423,19 +431,19 @@ 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);
-- 
2.20.1

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