[PATCH 2/4] drm/bridge: add bridge notifier to be notified of bridge addition and removal

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

In preparation for allowing bridges to be added to and removed from a DRM
card without destroying the whole card, add a DRM bridge notifier. Notified
events are addition and removal to/from the global bridge list.

Co-developed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
---
 drivers/gpu/drm/drm_bridge.c | 35 +++++++++++++++++++++++++++++++++++
 include/drm/drm_bridge.h     | 19 +++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 521a71c61b16..245f7fa4ea22 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -25,6 +25,7 @@
 #include <linux/media-bus-format.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/notifier.h>
 
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_bridge.h>
@@ -197,6 +198,36 @@
 
 static DEFINE_MUTEX(bridge_lock);
 static LIST_HEAD(bridge_list);
+static BLOCKING_NOTIFIER_HEAD(bridge_notifier);
+
+/**
+ * drm_bridge_notifier_register - add a DRM bridge notifier
+ * @nb: the notifier block to be registered
+ *
+ * The notifier block will be notified of events defined in
+ * &drm_bridge_notifier_event
+ */
+int drm_bridge_notifier_register(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&bridge_notifier, nb);
+}
+EXPORT_SYMBOL(drm_bridge_notifier_register);
+
+/**
+ * drm_bridge_notifier_unregister - remove a DRM bridge notifier
+ * @nb: the notifier block to be unregistered
+ */
+int drm_bridge_notifier_unregister(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&bridge_notifier, nb);
+}
+EXPORT_SYMBOL(drm_bridge_notifier_unregister);
+
+static void drm_bridge_notifier_notify(unsigned long event,
+				       struct drm_bridge *bridge)
+{
+	blocking_notifier_call_chain(&bridge_notifier, event, bridge);
+}
 
 /**
  * drm_bridge_add - add the given bridge to the global bridge list
@@ -210,6 +241,8 @@ void drm_bridge_add(struct drm_bridge *bridge)
 	mutex_lock(&bridge_lock);
 	list_add_tail(&bridge->list, &bridge_list);
 	mutex_unlock(&bridge_lock);
+
+	drm_bridge_notifier_notify(DRM_BRIDGE_NOTIFY_ADD, bridge);
 }
 EXPORT_SYMBOL(drm_bridge_add);
 
@@ -243,6 +276,8 @@ EXPORT_SYMBOL(devm_drm_bridge_add);
  */
 void drm_bridge_remove(struct drm_bridge *bridge)
 {
+	drm_bridge_notifier_notify(DRM_BRIDGE_NOTIFY_REMOVE, bridge);
+
 	mutex_lock(&bridge_lock);
 	list_del_init(&bridge->list);
 	mutex_unlock(&bridge_lock);
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 4baca0d9107b..ee48c1eb76ae 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -43,6 +43,22 @@ struct drm_panel;
 struct edid;
 struct i2c_adapter;
 
+/**
+ * enum drm_bridge_notifier_event - DRM bridge events
+ */
+enum drm_bridge_notifier_event {
+	/**
+	 * @DRM_BRIDGE_NOTIFY_ADD: A bridge has just been added to the
+	 * global bridge list. See drm_bridge_add().
+	 */
+	DRM_BRIDGE_NOTIFY_ADD,
+	/**
+	 * @DRM_BRIDGE_NOTIFY_REMOVE: A bridge is about to be removed from
+	 * the global bridge list. See drm_bridge_remove().
+	 */
+	DRM_BRIDGE_NOTIFY_REMOVE,
+};
+
 /**
  * enum drm_bridge_attach_flags - Flags for &drm_bridge_funcs.attach
  */
@@ -781,6 +797,9 @@ drm_priv_to_bridge(struct drm_private_obj *priv)
 	return container_of(priv, struct drm_bridge, base);
 }
 
+int drm_bridge_notifier_register(struct notifier_block *nb);
+int drm_bridge_notifier_unregister(struct notifier_block *nb);
+
 void drm_bridge_add(struct drm_bridge *bridge);
 int devm_drm_bridge_add(struct device *dev, struct drm_bridge *bridge);
 void drm_bridge_remove(struct drm_bridge *bridge);

-- 
2.34.1