diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 22f3bf5..53120a7 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -493,6 +493,12 @@
 	/* Dot clock in Hz: */
 	dotclock = (u64) crtc->hwmode.clock * 1000;
 
+	/* Fields of interlaced scanout modes are only halve a frame duration.
+	 * Double the dotclock to get halve the frame-/line-/pixelduration.
+	 */
+	if (crtc->hwmode.flags & DRM_MODE_FLAG_INTERLACE)
+		dotclock *= 2;
+
 	/* Valid dotclock? */
 	if (dotclock > 0) {
 		/* Convert scanline length in pixels and video dot clock to
@@ -605,14 +611,6 @@
 		return -EAGAIN;
 	}
 
-	/* Don't know yet how to handle interlaced or
-	 * double scan modes. Just no-op for now.
-	 */
-	if (mode->flags & (DRM_MODE_FLAG_INTERLACE | DRM_MODE_FLAG_DBLSCAN)) {
-		DRM_DEBUG("crtc %d: Noop due to unsupported mode.\n", crtc);
-		return -ENOTSUPP;
-	}
-
 	/* Get current scanout position with system timestamp.
 	 * Repeat query up to DRM_TIMESTAMP_MAXRETRIES times
 	 * if single query takes longer than max_error nanoseconds.