drm/exynos: release unhandled page flip events at postclose.

This patch resolves a dead lock issue that could be incurred when
exynos_drm_crtc_dpms function was called.

The exynos_drm_crtc_dpms function waits for the completion of pended
page flip events. However, preclose callback - this releases all unhandled
page flip events - is called prior to the exynos_drm_crtc_dpms function call
when drm is closed. So at this time, this will make the exynos_drm_crtc_dpms
to wait infiniately for the completion of the page flip events.

This patch releases the unhandled page flip events at postclose instead
of preclose so that exynos_drm_crtc_dpms function can be waked up.

Changelog v2:
- fix a memory leak when drm is closed.
  . it has a memory leak when a requeste page flip is handled after
    drm_events_release() is called and before drm_fb_release()
    is called. At this time, a drm_pending_event will not be freed.
    So also this chage releases the drm_pending_event at postclose().
    And it calls drm_vblank_put() for pair if there is any unhandled page
    flip event.
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_drv.c

@@ -172,29 +172,38 @@ static int exynos_drm_open(struct drm_device *dev, struct drm_file *file)
 
 static void exynos_drm_preclose(struct drm_device *dev,
 					struct drm_file *file)
+{
+	exynos_drm_subdrv_close(dev, file);
+}
+
+static void exynos_drm_postclose(struct drm_device *dev, struct drm_file *file)
 {
 	struct exynos_drm_private *private = dev->dev_private;
-	struct drm_pending_vblank_event *e, *t;
+	struct drm_pending_vblank_event *v, *vt;
+	struct drm_pending_event *e, *et;
 	unsigned long flags;
 
-	/* release events of current file */
+	if (!file->driver_priv)
+		return;
+
+	/* Release all events not unhandled by page flip handler. */
 	spin_lock_irqsave(&dev->event_lock, flags);
-	list_for_each_entry_safe(e, t, &private->pageflip_event_list,
+	list_for_each_entry_safe(v, vt, &private->pageflip_event_list,
 			base.link) {
-		if (e->base.file_priv == file) {
-			list_del(&e->base.link);
-			e->base.destroy(&e->base);
+		if (v->base.file_priv == file) {
+			list_del(&v->base.link);
+			drm_vblank_put(dev, v->pipe);
+			v->base.destroy(&v->base);
 		}
 	}
-	spin_unlock_irqrestore(&dev->event_lock, flags);
 
-	exynos_drm_subdrv_close(dev, file);
-}
+	/* Release all events handled by page flip handler but not freed. */
+	list_for_each_entry_safe(e, et, &file->event_list, link) {
+		list_del(&e->link);
+		e->destroy(e);
+	}
+	spin_unlock_irqrestore(&dev->event_lock, flags);
 
-static void exynos_drm_postclose(struct drm_device *dev, struct drm_file *file)
-{
-	if (!file->driver_priv)
-		return;
 
 	kfree(file->driver_priv);
 	file->driver_priv = NULL;