drm/i915: Make legacy cursor updates more unsynced

We're clearing the legacy_cursor_update flag before calling
drm_atomic_helper_setup_commit() which means the helper will
wait for the flip to complete before cleaning up the framebuffers.
That's not what we want for the legacy cursor, so let's clear
the flag after setting up the commit.

Also toss in a FIXME about solving these problems in a nicer
way using the fabled vblank workers.

v2: Also unsync with legacy page flips

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Uwe Kleine-König <uwe@kleine-koenig.org>
Cc: Rafael Ristovski <rafael.ristovski@gmail.com>
Fixes: a5509abda48e ("drm/i915: Fix legacy cursor vs. watermarks for ILK-BDW")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170329142123.5923-1-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
(cherry picked from commit 895203044067af64400cedbc055898bcec98d102)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -13007,17 +13007,6 @@ static int intel_atomic_commit(struct drm_device *dev,
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	int ret = 0;
 
-	/*
-	 * The intel_legacy_cursor_update() fast path takes care
-	 * of avoiding the vblank waits for simple cursor
-	 * movement and flips. For cursor on/off and size changes,
-	 * we want to perform the vblank waits so that watermark
-	 * updates happen during the correct frames. Gen9+ have
-	 * double buffered watermarks and so shouldn't need this.
-	 */
-	if (INTEL_GEN(dev_priv) < 9)
-		state->legacy_cursor_update = false;
-
 	ret = drm_atomic_helper_setup_commit(state, nonblock);
 	if (ret)
 		return ret;
@@ -13033,6 +13022,26 @@ static int intel_atomic_commit(struct drm_device *dev,
 		return ret;
 	}
 
+	/*
+	 * The intel_legacy_cursor_update() fast path takes care
+	 * of avoiding the vblank waits for simple cursor
+	 * movement and flips. For cursor on/off and size changes,
+	 * we want to perform the vblank waits so that watermark
+	 * updates happen during the correct frames. Gen9+ have
+	 * double buffered watermarks and so shouldn't need this.
+	 *
+	 * Do this after drm_atomic_helper_setup_commit() and
+	 * intel_atomic_prepare_commit() because we still want
+	 * to skip the flip and fb cleanup waits. Although that
+	 * does risk yanking the mapping from under the display
+	 * engine.
+	 *
+	 * FIXME doing watermarks and fb cleanup from a vblank worker
+	 * (assuming we had any) would solve these problems.
+	 */
+	if (INTEL_GEN(dev_priv) < 9)
+		state->legacy_cursor_update = false;
+
 	drm_atomic_helper_swap_state(state, true);
 	dev_priv->wm.distrust_bios_wm = false;
 	intel_shared_dpll_swap_state(state);