drm/bridge: Make (pre/post) enable/disable callbacks optional

Instead of forcing bridges to implement empty callbacks make them all
optional.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/drm_bridge.c

@@ -186,7 +186,8 @@ void drm_bridge_disable(struct drm_bridge *bridge)
 
 	drm_bridge_disable(bridge->next);
 
-	bridge->funcs->disable(bridge);
+	if (bridge->funcs->disable)
+		bridge->funcs->disable(bridge);
 }
 EXPORT_SYMBOL(drm_bridge_disable);
 
@@ -206,7 +207,8 @@ void drm_bridge_post_disable(struct drm_bridge *bridge)
 	if (!bridge)
 		return;
 
-	bridge->funcs->post_disable(bridge);
+	if (bridge->funcs->post_disable)
+		bridge->funcs->post_disable(bridge);
 
 	drm_bridge_post_disable(bridge->next);
 }
@@ -256,7 +258,8 @@ void drm_bridge_pre_enable(struct drm_bridge *bridge)
 
 	drm_bridge_pre_enable(bridge->next);
 
-	bridge->funcs->pre_enable(bridge);
+	if (bridge->funcs->pre_enable)
+		bridge->funcs->pre_enable(bridge);
 }
 EXPORT_SYMBOL(drm_bridge_pre_enable);
 
@@ -276,7 +279,8 @@ void drm_bridge_enable(struct drm_bridge *bridge)
 	if (!bridge)
 		return;
 
-	bridge->funcs->enable(bridge);
+	if (bridge->funcs->enable)
+		bridge->funcs->enable(bridge);
 
 	drm_bridge_enable(bridge->next);
 }

include/drm/drm_crtc.h

@@ -1581,6 +1581,8 @@ struct drm_bridge_funcs {
 	 *
 	 * The bridge can assume that the display pipe (i.e. clocks and timing
 	 * signals) feeding it is still running when this callback is called.
+	 *
+	 * The disable callback is optional.
 	 */
 	void (*disable)(struct drm_bridge *bridge);
 
@@ -1597,6 +1599,8 @@ struct drm_bridge_funcs {
 	 * The bridge must assume that the display pipe (i.e. clocks and timing
 	 * singals) feeding it is no longer running when this callback is
 	 * called.
+	 *
+	 * The post_disable callback is optional.
 	 */
 	void (*post_disable)(struct drm_bridge *bridge);
 
@@ -1625,6 +1629,8 @@ struct drm_bridge_funcs {
 	 * will not yet be running when this callback is called. The bridge must
 	 * not enable the display link feeding the next bridge in the chain (if
 	 * there is one) when this callback is called.
+	 *
+	 * The pre_enable callback is optional.
 	 */
 	void (*pre_enable)(struct drm_bridge *bridge);
 
@@ -1642,6 +1648,8 @@ struct drm_bridge_funcs {
 	 * signals) feeding it is running when this callback is called. This
 	 * callback must enable the display link feeding the next bridge in the
 	 * chain if there is one.
+	 *
+	 * The enable callback is optional.
 	 */
 	void (*enable)(struct drm_bridge *bridge);
 };