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Message-Id: <20251112-drm-bridge-atomic-vs-remove-v3-1-85db717ce094@bootlin.com>
Date: Wed, 12 Nov 2025 17:34:34 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Maxime Ripard <mripard@...nel.org>, Simona Vetter <simona@...ll.ch>,
Andrzej Hajda <andrzej.hajda@...el.com>,
Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
Luca Ceresoli <luca.ceresoli@...tlin.com>,
Dmitry Baryshkov <lumag@...nel.org>
Subject: [PATCH v3 1/2] 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@...nel.org>
Link: https://lore.kernel.org/all/20250106-vigorous-talented-viper-fa49d9@houat/
Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
Changes in v3:
- call drm_bridge_remove() in drm_bridge_unplug()
- Fixed kerneldoc variable names (reported here:
https://lore.kernel.org/lkml/202509271654.j3IsjsAJ-lkp@intel.com/)
---
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
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