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>

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 6d2d4fa..22f3bf5 100644 (file)
--- 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);