Index: dev/drm/drm_sysctl.c
===================================================================
--- dev/drm/drm_sysctl.c	(revision 190402)
+++ dev/drm/drm_sysctl.c	(working copy)
@@ -38,6 +38,7 @@
 static int	   drm_vm_info DRM_SYSCTL_HANDLER_ARGS;
 static int	   drm_clients_info DRM_SYSCTL_HANDLER_ARGS;
 static int	   drm_bufs_info DRM_SYSCTL_HANDLER_ARGS;
+static int	   drm_vblank_info DRM_SYSCTL_HANDLER_ARGS;
 
 struct drm_sysctl_list {
 	const char *name;
@@ -47,6 +48,7 @@
 	{"vm",	    drm_vm_info},
 	{"clients", drm_clients_info},
 	{"bufs",    drm_bufs_info},
+	{"vblank",    drm_vblank_info},
 };
 #define DRM_SYSCTL_ENTRIES (sizeof(drm_sysctl_list)/sizeof(drm_sysctl_list[0]))
 
@@ -313,3 +315,25 @@
 	free(tempprivs, DRM_MEM_DRIVER);
 	return retcode;
 }
+
+static int drm_vblank_info DRM_SYSCTL_HANDLER_ARGS
+{
+	struct drm_device *dev = arg1;
+	char buf[128];
+	int retcode;
+	int i;
+
+	DRM_SYSCTL_PRINT("\ncrtc ref count    last     enabled inmodeset\n");
+	for(i = 0 ; i < dev->num_crtcs ; i++) {
+		DRM_SYSCTL_PRINT("  %02d  %02d %08d %08d %02d      %02d\n",
+		    i, atomic_read(&dev->vblank[i].refcount),
+		    atomic_read(&dev->vblank[i].count),
+		    atomic_read(&dev->vblank[i].last),
+		    atomic_read(&dev->vblank[i].enabled),
+		    atomic_read(&dev->vblank[i].inmodeset));
+	}
+
+	SYSCTL_OUT(req, "", -1);
+done:
+	return retcode;
+}
Index: dev/drm/drm_irq.c
===================================================================
--- dev/drm/drm_irq.c	(revision 190433)
+++ dev/drm/drm_irq.c	(working copy)
@@ -345,13 +345,11 @@
 	struct drm_modeset_ctl *modeset = data;
 	int crtc, ret = 0;
 
-	DRM_DEBUG("num_crtcs=%d\n", dev->num_crtcs);
 	/* If drm_vblank_init() hasn't been called yet, just no-op */
 	if (!dev->num_crtcs)
 		goto out;
 
 	crtc = modeset->crtc;
-	DRM_DEBUG("crtc=%d\n", crtc);
 	if (crtc >= dev->num_crtcs) {
 		ret = EINVAL;
 		goto out;
@@ -366,7 +364,7 @@
 	 */
 	switch (modeset->cmd) {
 	case _DRM_PRE_MODESET:
-		DRM_DEBUG("pre-modeset\n");
+		DRM_DEBUG("pre-modeset, crtc %d\n", crtc);
 		if (!dev->vblank[crtc].inmodeset) {
 			dev->vblank[crtc].inmodeset = 0x1;
 			if (drm_vblank_get(dev, crtc) == 0)
@@ -374,7 +372,7 @@
 		}
 		break;
 	case _DRM_POST_MODESET:
-		DRM_DEBUG("post-modeset\n");
+		DRM_DEBUG("post-modeset, crtc %d\n", crtc);
 		if (dev->vblank[crtc].inmodeset) {
 			DRM_SPINLOCK(&dev->vbl_lock);
 			dev->vblank_disable_allowed = 1;
@@ -477,6 +475,9 @@
 			mtx_unlock(&dev->irq_lock);
 		}
 
+		if (ret == EWOULDBLOCK)
+			DRM_ERROR("timed out waiting on vblank\n");
+
 		if (ret != EINTR && ret != ERESTART) {
 			struct timeval now;
 
Index: dev/drm/i915_irq.c
===================================================================
--- dev/drm/i915_irq.c	(revision 190402)
+++ dev/drm/i915_irq.c	(working copy)
@@ -205,7 +205,7 @@
 	iir = I915_READ(IIR);
 
 	if (IS_I965G(dev)) {
-		vblank_status = I915_START_VBLANK_INTERRUPT_STATUS;
+		vblank_status = PIPE_START_VBLANK_INTERRUPT_STATUS;
 		vblank_enable = PIPE_START_VBLANK_INTERRUPT_ENABLE;
 	} else {
 		vblank_status = I915_VBLANK_INTERRUPT_STATUS;
@@ -343,6 +343,7 @@
 
 	DRM_DEBUG("irq_nr=%d breadcrumb=%d\n", irq_nr,
 		  READ_BREADCRUMB(dev_priv));
+	DRM_DEBUG("ier: %08x, imr: %08x\n", I915_READ(IER), I915_READ(IER));
 
 	i915_user_irq_get(dev);
 	DRM_WAIT_ON(ret, dev_priv->irq_queue, 3 * DRM_HZ,