drm/exynos: make zpos property immutable

We already set each plane zpos at init, after that changes to zpos are
not expected. This patch turns zpos into a read-only property so now it is
impossible to set zpos.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_plane.c

@@ -184,27 +184,10 @@ static void exynos_plane_destroy(struct drm_plane *plane)
 	drm_plane_cleanup(plane);
 }
 
-static int exynos_plane_set_property(struct drm_plane *plane,
-				     struct drm_property *property,
-				     uint64_t val)
-{
-	struct drm_device *dev = plane->dev;
-	struct exynos_drm_plane *exynos_plane = to_exynos_plane(plane);
-	struct exynos_drm_private *dev_priv = dev->dev_private;
-
-	if (property == dev_priv->plane_zpos_property) {
-		exynos_plane->zpos = val;
-		return 0;
-	}
-
-	return -EINVAL;
-}
-
 static struct drm_plane_funcs exynos_plane_funcs = {
 	.update_plane	= exynos_update_plane,
 	.disable_plane	= exynos_disable_plane,
 	.destroy	= exynos_plane_destroy,
-	.set_property	= exynos_plane_set_property,
 };
 
 static void exynos_plane_attach_zpos_property(struct drm_plane *plane,
@@ -216,8 +199,8 @@ static void exynos_plane_attach_zpos_property(struct drm_plane *plane,
 
 	prop = dev_priv->plane_zpos_property;
 	if (!prop) {
-		prop = drm_property_create_range(dev, 0, "zpos", 0,
-						 MAX_PLANE - 1);
+		prop = drm_property_create_range(dev, DRM_MODE_PROP_IMMUTABLE,
+						 "zpos", 0, MAX_PLANE - 1);
 		if (!prop)
 			return;