drm/bridge: add drm_bridge_unplug() and drm_bridge_enter/exit()

To allow DRM bridges to be removable, add synchronization functions
allowing to tell when a bridge hardware has been physically unplugged and
to mark a critical section that should not be entered after that.

This is inspired by the drm_dev_unplugged/enter/exit() functions for struct
drm_device.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/all/20250106-vigorous-talented-viper-fa49d9@houat/
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patch.msgid.link/20251112-drm-bridge-atomic-vs-remove-v3-1-85db717ce094@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 8f355df883d8ac8de9d361ec302f4ccbf3bca0d6..db40c26d1cb354f818f12a5a53f9baa6a7fc3574 100644 (file)
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -27,6 +27,7 @@
 #include <linux/media-bus-format.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/srcu.h>
 
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_bridge.h>
@@ -202,6 +203,67 @@ static DEFINE_MUTEX(bridge_lock);
 static LIST_HEAD(bridge_list);
 static LIST_HEAD(bridge_lingering_list);
 
+DEFINE_STATIC_SRCU(drm_bridge_unplug_srcu);
+
+/**
+ * drm_bridge_enter - Enter DRM bridge critical section
+ * @bridge: DRM bridge
+ * @idx: Pointer to index that will be passed to the matching drm_bridge_exit()
+ *
+ * This function marks and protects the beginning of a section that should not
+ * be entered after the bridge has been unplugged. The section end is marked
+ * with drm_bridge_exit(). Calls to this function can be nested.
+ *
+ * Returns:
+ * True if it is OK to enter the section, false otherwise.
+ */
+bool drm_bridge_enter(struct drm_bridge *bridge, int *idx)
+{
+       *idx = srcu_read_lock(&drm_bridge_unplug_srcu);
+
+       if (bridge->unplugged) {
+               srcu_read_unlock(&drm_bridge_unplug_srcu, *idx);
+               return false;
+       }
+
+       return true;
+}
+EXPORT_SYMBOL(drm_bridge_enter);
+
+/**
+ * drm_bridge_exit - Exit DRM bridge critical section
+ * @idx: index returned by drm_bridge_enter()
+ *
+ * This function marks the end of a section that should not be entered after
+ * the bridge has been unplugged.
+ */
+void drm_bridge_exit(int idx)
+{
+       srcu_read_unlock(&drm_bridge_unplug_srcu, idx);
+}
+EXPORT_SYMBOL(drm_bridge_exit);
+
+/**
+ * drm_bridge_unplug - declare a DRM bridge was unplugged and remove it
+ * @bridge: DRM bridge
+ *
+ * This tells the bridge has been physically unplugged and no operations on
+ * device resources must be done anymore. Entry-points can use
+ * drm_bridge_enter() and drm_bridge_exit() to protect device resources in
+ * a race free manner.
+ *
+ * Also unregisters the bridge.
+ */
+void drm_bridge_unplug(struct drm_bridge *bridge)
+{
+       bridge->unplugged = true;
+
+       synchronize_srcu(&drm_bridge_unplug_srcu);
+
+       drm_bridge_remove(bridge);
+}
+EXPORT_SYMBOL(drm_bridge_unplug);
+
 static void __drm_bridge_free(struct kref *kref)
 {
        struct drm_bridge *bridge = container_of(kref, struct drm_bridge, refcount);

diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 0ff7ab4aa8689a022458f935a7ffb23a2b715802..d2683846cc619007f85a6f605b9d23ce971e04b3 100644 (file)
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -1143,6 +1143,14 @@ struct drm_bridge {
         */
        struct kref refcount;
 
+       /**
+        * @unplugged:
+        *
+        * Flag to tell if the bridge has been unplugged.
+        * See drm_bridge_enter() and drm_bridge_unplug().
+        */
+       bool unplugged;
+
        /** @driver_private: pointer to the bridge driver's internal context */
        void *driver_private;
        /** @ops: bitmask of operations supported by the bridge */
@@ -1278,6 +1286,10 @@ drm_priv_to_bridge(struct drm_private_obj *priv)
        return container_of(priv, struct drm_bridge, base);
 }
 
+bool drm_bridge_enter(struct drm_bridge *bridge, int *idx);
+void drm_bridge_exit(int idx);
+void drm_bridge_unplug(struct drm_bridge *bridge);
+
 struct drm_bridge *drm_bridge_get(struct drm_bridge *bridge);
 void drm_bridge_put(struct drm_bridge *bridge);