In preparation for allowing bridges to be added to and removed from a DRM
card without destroying the whole card, add a new DRM bridge function
called on addition and removal of bridges.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
 drivers/gpu/drm/drm_bridge.c | 12 ++++++++++++
 include/drm/drm_bridge.h     | 23 +++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index d44f055dbe3e..c98117f1abec 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -205,8 +205,14 @@ static LIST_HEAD(bridge_list);
  */
 void drm_bridge_add(struct drm_bridge *bridge)
 {
+	struct drm_bridge *br, *tmp;
+
 	mutex_init(&bridge->hpd_mutex);
 
+	list_for_each_entry_safe(br, tmp, &bridge_list, list)
+		if (br->funcs->bridge_event_notify)
+			br->funcs->bridge_event_notify(br, DRM_EVENT_BRIDGE_ADD, bridge);
+
 	mutex_lock(&bridge_lock);
 	list_add_tail(&bridge->list, &bridge_list);
 	mutex_unlock(&bridge_lock);
@@ -243,10 +249,16 @@ EXPORT_SYMBOL(devm_drm_bridge_add);
  */
 void drm_bridge_remove(struct drm_bridge *bridge)
 {
+	struct drm_bridge *br, *tmp;
+
 	mutex_lock(&bridge_lock);
 	list_del_init(&bridge->list);
 	mutex_unlock(&bridge_lock);
 
+	list_for_each_entry_safe(br, tmp, &bridge_list, list)
+		if (br->funcs->bridge_event_notify)
+			br->funcs->bridge_event_notify(br, DRM_EVENT_BRIDGE_REMOVE, bridge);
+
 	mutex_destroy(&bridge->hpd_mutex);
 }
 EXPORT_SYMBOL(drm_bridge_remove);
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 75019d16be64..635cc24bdeba 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -54,6 +54,11 @@ enum drm_bridge_attach_flags {
 	DRM_BRIDGE_ATTACH_NO_CONNECTOR = BIT(0),
 };
 
+enum drm_bridge_event_type {
+	DRM_EVENT_BRIDGE_ADD,
+	DRM_EVENT_BRIDGE_REMOVE,
+};
+
 /**
  * struct drm_bridge_funcs - drm_bridge control functions
  */
@@ -676,6 +681,24 @@ struct drm_bridge_funcs {
 				    enum hdmi_infoframe_type type,
 				    const u8 *buffer, size_t len);
 
+	/**
+	 * @bridge_event_notify:
+	 *
+	 * Notify that another bridge is being added or removed.
+	 *
+	 * This callback is optional. Bridges implementing it must always
+	 * check whether the event refers to a bridge they actually need to
+	 * interact with.
+	 *
+	 * @bridge: bridge being notified
+	 * @event: event happened (add/remove bridge)
+	 * @new_bridge: the bridge mentioned by the event (i.e. the bridge
+	 *              being added or removed)
+	 */
+	void (*bridge_event_notify)(struct drm_bridge *bridge,
+				    enum drm_bridge_event_type event,
+				    struct drm_bridge *event_bridge);
+
 	/**
 	 * @debugfs_init:
 	 *

-- 
2.34.1