drm: add support for private planes

In cases where the scanout hw is sufficiently similar between "overlay"
and traditional crtc layers, it might be convenient to allow the driver
to create internal drm_plane helper objects used by the drm_crtc
implementation, rather than duplicate code between the plane and crtc.
A private plane is not exposed to userspace.

Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -557,7 +557,8 @@ EXPORT_SYMBOL(drm_encoder_cleanup);
 int drm_plane_init(struct drm_device *dev, struct drm_plane *plane,
 		   unsigned long possible_crtcs,
 		   const struct drm_plane_funcs *funcs,
-		   const uint32_t *formats, uint32_t format_count)
+		   const uint32_t *formats, uint32_t format_count,
+		   bool priv)
 {
 	mutex_lock(&dev->mode_config.mutex);
 
@@ -577,8 +578,16 @@ int drm_plane_init(struct drm_device *dev, struct drm_plane *plane,
 	plane->format_count = format_count;
 	plane->possible_crtcs = possible_crtcs;
 
-	list_add_tail(&plane->head, &dev->mode_config.plane_list);
-	dev->mode_config.num_plane++;
+	/* private planes are not exposed to userspace, but depending on
+	 * display hardware, might be convenient to allow sharing programming
+	 * for the scanout engine with the crtc implementation.
+	 */
+	if (!priv) {
+		list_add_tail(&plane->head, &dev->mode_config.plane_list);
+		dev->mode_config.num_plane++;
+	} else {
+		INIT_LIST_HEAD(&plane->head);
+	}
 
 	mutex_unlock(&dev->mode_config.mutex);
 
@@ -593,8 +602,11 @@ void drm_plane_cleanup(struct drm_plane *plane)
 	mutex_lock(&dev->mode_config.mutex);
 	kfree(plane->format_types);
 	drm_mode_object_put(dev, &plane->base);
-	list_del(&plane->head);
-	dev->mode_config.num_plane--;
+	/* if not added to a list, it must be a private plane */
+	if (!list_empty(&plane->head)) {
+		list_del(&plane->head);
+		dev->mode_config.num_plane--;
+	}
 	mutex_unlock(&dev->mode_config.mutex);
 }
 EXPORT_SYMBOL(drm_plane_cleanup);