drm: Correct unbalanced drm_vblank_put() during mode setting.

The first time we install a mode, the vblank will be disabled for a pipe
and so drm_vblank_get() in drm_vblank_pre_modeset() will fail. As we
unconditionally call drm_vblank_put() afterwards, the vblank reference
counter becomes unbalanced.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 3795dbc0f50c..93e677a481f5 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -435,6 +435,8 @@ EXPORT_SYMBOL(drm_vblank_get);
  */
 void drm_vblank_put(struct drm_device *dev, int crtc)
 {
+        BUG_ON (atomic_read (&dev->vblank_refcount[crtc]) == 0);
+
         /* Last user schedules interrupt disable */
         if (atomic_dec_and_test(&dev->vblank_refcount[crtc]))
                 mod_timer(&dev->vblank_disable_timer, jiffies + 5*DRM_HZ);
@@ -460,8 +462,9 @@ void drm_vblank_pre_modeset(struct drm_device *dev, int crtc)
          * so that interrupts remain enabled in the interim.
          */
         if (!dev->vblank_inmodeset[crtc]) {
-                dev->vblank_inmodeset[crtc] = 1;
-                drm_vblank_get(dev, crtc);
+                dev->vblank_inmodeset[crtc] = 0x1;
+                if (drm_vblank_get(dev, crtc) == 0)
+                        dev->vblank_inmodeset[crtc] |= 0x2;
         }
 }
 EXPORT_SYMBOL(drm_vblank_pre_modeset);
@@ -473,9 +476,12 @@ void drm_vblank_post_modeset(struct drm_device *dev, int crtc)
         if (dev->vblank_inmodeset[crtc]) {
                 spin_lock_irqsave(&dev->vbl_lock, irqflags);
                 dev->vblank_disable_allowed = 1;
-                dev->vblank_inmodeset[crtc] = 0;
                 spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
-                drm_vblank_put(dev, crtc);
+
+                if (dev->vblank_inmodeset[crtc] & 0x2)
+                        drm_vblank_put(dev, crtc);
+
+                dev->vblank_inmodeset[crtc] = 0;
         }
 }
 EXPORT_SYMBOL(drm_vblank_post_modeset);