drm/i915: Use ring->flush() instead of MI_FLUSH

Use the ring abstraction to hide the details of having choose the
appropriate flushing method.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c3f0400..0505ddb 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5056,24 +5056,23 @@
 	atomic_inc(&obj_priv->pending_flip);
 	work->pending_flip_obj = obj;
 
-	if (was_dirty || IS_GEN3(dev) || IS_GEN2(dev)) {
+	/* Schedule the pipelined flush */
+	if (was_dirty)
+		i915_gem_flush_ring(dev, obj_priv->ring, 0, was_dirty);
+
+	if (IS_GEN3(dev) || IS_GEN2(dev)) {
+		u32 flip_mask;
+
+		/* Can't queue multiple flips, so wait for the previous
+		 * one to finish before executing the next.
+		 */
 		BEGIN_LP_RING(2);
-		if (IS_GEN3(dev) || IS_GEN2(dev)) {
-			u32 flip_mask;
-
-			/* Can't queue multiple flips, so wait for the previous
-			 * one to finish before executing the next.
-			 */
-
-			if (intel_crtc->plane)
-				flip_mask = MI_WAIT_FOR_PLANE_B_FLIP;
-			else
-				flip_mask = MI_WAIT_FOR_PLANE_A_FLIP;
-
-			OUT_RING(MI_WAIT_FOR_EVENT | flip_mask);
-		} else
-			OUT_RING(MI_NOOP);
-		OUT_RING(MI_FLUSH);
+		if (intel_crtc->plane)
+			flip_mask = MI_WAIT_FOR_PLANE_B_FLIP;
+		else
+			flip_mask = MI_WAIT_FOR_PLANE_A_FLIP;
+		OUT_RING(MI_WAIT_FOR_EVENT | flip_mask);
+		OUT_RING(MI_NOOP);
 		ADVANCE_LP_RING();
 	}