drm/sti: Let core take care of normalizing the zpos

Instead of re-implementing the drm_atomic_helper_check() locally with just
adding drm_atomic_normalize_zpos() into it, set the
drm_mode_config->normalize_zpos.

Note: the drm_atomic_helper_check() now includes

if (state->legacy_cursor_update)
	state->async_update = !drm_atomic_helper_async_check(drm, state);

which was added after the driver moved away from using it
(38d868e41c4b9250d5a115c049dc2d48f4909581 drm: Don't force all planes to
be added to the state due to zpos)

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
CC: Benjamin Gaignard <benjamin.gaignard@linaro.org>
CC: Vincent Abriou <vincent.abriou@st.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180321102029.15248-5-peter.ujfalusi@ti.com

drivers/gpu/drm/sti/sti_drv.c

@@ -119,30 +119,10 @@ err:
 	return ret;
 }
 
-static int sti_atomic_check(struct drm_device *dev,
-			    struct drm_atomic_state *state)
-{
-	int ret;
-
-	ret = drm_atomic_helper_check_modeset(dev, state);
-	if (ret)
-		return ret;
-
-	ret = drm_atomic_normalize_zpos(dev, state);
-	if (ret)
-		return ret;
-
-	ret = drm_atomic_helper_check_planes(dev, state);
-	if (ret)
-		return ret;
-
-	return ret;
-}
-
 static const struct drm_mode_config_funcs sti_mode_config_funcs = {
 	.fb_create = drm_gem_fb_create,
 	.output_poll_changed = drm_fb_helper_output_poll_changed,
-	.atomic_check = sti_atomic_check,
+	.atomic_check = drm_atomic_helper_check,
 	.atomic_commit = drm_atomic_helper_commit,
 };
 
@@ -160,6 +140,8 @@ static void sti_mode_config_init(struct drm_device *dev)
 	dev->mode_config.max_height = STI_MAX_FB_HEIGHT;
 
 	dev->mode_config.funcs = &sti_mode_config_funcs;
+
+	dev->mode_config.normalize_zpos = true;
 }
 
 DEFINE_DRM_GEM_CMA_FOPS(sti_driver_fops);