drm/exynos: use wait_event_timeout() for safety usage

There could be the case that the page flip operation isn't finished correctly
with some abnormal condition such as panel reset. So this patch replaces
wait_event() with wait_event_timeout() to avoid waiting for page flip completion
infinitely.
And clears exynos_crtc->pending_flip in exynos_drm_crtc_page_flip()
when exynos_drm_crtc_mode_set_commit() is failed.

Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
Acked-by: Inki Dae <inki.dae@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_crtc.c

@@ -69,8 +69,10 @@ static void exynos_drm_crtc_dpms(struct drm_crtc *crtc, int mode)
 
 	if (mode > DRM_MODE_DPMS_ON) {
 		/* wait for the completion of page flip. */
-		wait_event(exynos_crtc->pending_flip_queue,
-				atomic_read(&exynos_crtc->pending_flip) == 0);
+		if (!wait_event_timeout(exynos_crtc->pending_flip_queue,
+				!atomic_read(&exynos_crtc->pending_flip),
+				HZ/20))
+			atomic_set(&exynos_crtc->pending_flip, 0);
 		drm_vblank_off(crtc->dev, exynos_crtc->pipe);
 	}
 
@@ -259,6 +261,7 @@ static int exynos_drm_crtc_page_flip(struct drm_crtc *crtc,
 			spin_lock_irq(&dev->event_lock);
 			drm_vblank_put(dev, exynos_crtc->pipe);
 			list_del(&event->base.link);
+			atomic_set(&exynos_crtc->pending_flip, 0);
 			spin_unlock_irq(&dev->event_lock);
 
 			goto out;