drm/vblank: Use memory barriers optimized for atomic_t instead of generics.

Documentation/atomic_ops.txt tells us that there are memory
barriers optimized for atomic_inc and other atomic_t ops.

Use these instead of smp_wmb(), and also to make the required
memory barriers around vblank counter increments more explicit.

Signed-off-by: Mario Kleiner <mario.kleiner@tuebingen.mpg.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 6d2d4faf8678..22f3bf5ecbd2 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -164,8 +164,10 @@ static void vblank_disable_and_save(struct drm_device *dev, int crtc)
          * available. In that case we can't account for this and just
          * hope for the best.
          */
-        if ((vblrc > 0) && (abs64(diff_ns) > 1000000))
+        if ((vblrc > 0) && (abs64(diff_ns) > 1000000)) {
                 atomic_inc(&dev->_vblank_count[crtc]);
+                smp_mb__after_atomic_inc();
+        }
 
         /* Invalidate all timestamps while vblank irq's are off. */
         clear_vblank_timestamps(dev, crtc);
@@ -858,10 +860,11 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc)
         if (rc) {
                 tslot = atomic_read(&dev->_vblank_count[crtc]) + diff;
                 vblanktimestamp(dev, crtc, tslot) = t_vblank;
-                smp_wmb();
         }
 
+        smp_mb__before_atomic_inc();
         atomic_add(diff, &dev->_vblank_count[crtc]);
+        smp_mb__after_atomic_inc();
 }
 
 /**
@@ -1296,12 +1299,13 @@ bool drm_handle_vblank(struct drm_device *dev, int crtc)
         if (abs64(diff_ns) > DRM_REDUNDANT_VBLIRQ_THRESH_NS) {
                 /* Store new timestamp in ringbuffer. */
                 vblanktimestamp(dev, crtc, vblcount + 1) = tvblank;
-                smp_wmb();
 
                 /* Increment cooked vblank count. This also atomically commits
                  * the timestamp computed above.
                  */
+                smp_mb__before_atomic_inc();
                 atomic_inc(&dev->_vblank_count[crtc]);
+                smp_mb__after_atomic_inc();
         } else {
                 DRM_DEBUG("crtc %d: Redundant vblirq ignored. diff_ns = %d\n",
                           crtc, (int) diff_ns);