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 <[email protected]> Link: https://lore.kernel.org/all/20250106-vigorous-talented-viper-fa49d9@houat/ Signed-off-by: Luca Ceresoli <[email protected]> --- Changes in v3: - call drm_bridge_remove() in drm_bridge_unplug() - Fixed kerneldoc variable names (reported here: https://lore.kernel.org/lkml/[email protected]/) --- drivers/gpu/drm/drm_bridge.c | 62 ++++++++++++++++++++++++++++++++++++++++++++ include/drm/drm_bridge.h | 12 +++++++++ 2 files changed, 74 insertions(+) diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index 8f355df883d8ac8de9d361ec302f4ccbf3bca0d6..db40c26d1cb354f818f12a5a53f9baa6a7fc3574 100644 --- 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 --- 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); -- 2.51.1
