Between drm_bridge_add() and drm_bridge_remove() bridges are "published" to
the DRM core via the global bridge_list and visible in
/sys/kernel/debug/dri/bridges. However between drm_bridge_remove() and the
last drm_bridge_put() memory is still allocated even though the bridge is
not "published", i.e. not in bridges_list, and also not visible in
debugfs. This prevents debugging refcounted bridges lifetime, especially
leaks due to any missing drm_bridge_put().
In order to allow debugfs to also show the removed bridges, move such
bridges into a new ad-hoc list until they are eventually freed.
Note this requires adding INIT_LIST_HEAD(&bridge->list) in the bridge
initialization code. The lack of such init was not exposing any bug so far,
but it would with the new code, for example when a bridge is allocated and
then freed without calling drm_bridge_add(), which is common on probe
errors.
Document the new behaviour of drm_bridge_remove() and update the
drm_bridge_add() documentation to stay consistent.
drm_bridge_add() needs special care for bridges being added after having
been previously added and then removed. This happens for example for many
non-DCS DSI host bridge drivers like samsung-dsim which
drm_bridge_add/remove() themselves every time the DSI device does a DSI
attaches/detach. When the DSI device is hot-pluggable this happens multiple
times in the lifetime of the DSI host bridge. When this happens, the
bridge->list is found in the removed list, not at the initialized state as
drm_bridge_add() currently expects.
Signed-off-by: Luca Ceresoli <luca.ceres...@bootlin.com>
---
Changes in v7:
- rebase on current drm-misc-next
- remove if (drm_bridge_is_refcounted(bridge)), refcounting is now
mandatory
- add check to detect when re-adding a bridge that is in the removed list
- improve commit message
- fix typo
This patch was added in v6.
---
drivers/gpu/drm/drm_bridge.c | 30 +++++++++++++++++++++++++++---
1 file changed, 27 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index
36e0829d25c29457cff5da5fec99646c74b6ad5a..2e688ee14b9efbc810bcdb0ab7ecd4b688be8299
100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -197,15 +197,22 @@
* driver.
*/
+/* Protect bridge_list and bridge_removed_list */
static DEFINE_MUTEX(bridge_lock);
static LIST_HEAD(bridge_list);
+static LIST_HEAD(bridge_removed_list);
static void __drm_bridge_free(struct kref *kref)
{
struct drm_bridge *bridge = container_of(kref, struct drm_bridge,
refcount);
+ mutex_lock(&bridge_lock);
+ list_del(&bridge->list);
+ mutex_unlock(&bridge_lock);
+
if (bridge->funcs->destroy)
bridge->funcs->destroy(bridge);
+
kfree(bridge->container);
}
@@ -275,6 +282,7 @@ void *__devm_drm_bridge_alloc(struct device *dev, size_t
size, size_t offset,
return ERR_PTR(-ENOMEM);
bridge = container + offset;
+ INIT_LIST_HEAD(&bridge->list);
bridge->container = container;
bridge->funcs = funcs;
kref_init(&bridge->refcount);
@@ -288,10 +296,13 @@ void *__devm_drm_bridge_alloc(struct device *dev, size_t
size, size_t offset,
EXPORT_SYMBOL(__devm_drm_bridge_alloc);
/**
- * drm_bridge_add - add the given bridge to the global bridge list
+ * drm_bridge_add - publish a bridge
*
* @bridge: bridge control structure
*
+ * Add the given bridge to the global list of "published" bridges, where
+ * they can be found by users via of_drm_find_bridge().
+ *
* The bridge to be added must have been allocated by
* devm_drm_bridge_alloc().
*/
@@ -304,6 +315,14 @@ void drm_bridge_add(struct drm_bridge *bridge)
drm_bridge_get(bridge);
+ /*
+ * If the bridge was previously added and then removed, it is now
+ * in bridge_removed_list. Remove it or bridge_removed_list will be
+ * corrupted when adding this bridge to bridge_list below.
+ */
+ if (!list_empty(&bridge->list))
+ list_del_init(&bridge->list);
+
mutex_init(&bridge->hpd_mutex);
if (bridge->ops & DRM_BRIDGE_OP_HDMI)
@@ -344,9 +363,14 @@ int devm_drm_bridge_add(struct device *dev, struct
drm_bridge *bridge)
EXPORT_SYMBOL(devm_drm_bridge_add);
/**
- * drm_bridge_remove - remove the given bridge from the global bridge list
+ * drm_bridge_remove - unpublish a bridge
*
* @bridge: bridge control structure
+ *
+ * Remove the given bridge from the global list of "published" bridges,
+ * so it won't be found by users via of_drm_find_bridge(), and add it to
+ * the removed bridge list, to keep track of removed bridges until their
+ * allocated memory is actually freed.
*/
void drm_bridge_remove(struct drm_bridge *bridge)
{
@@ -357,7 +381,7 @@ void drm_bridge_remove(struct drm_bridge *bridge)
br->funcs->bridge_event_notify(br,
DRM_EVENT_BRIDGE_REMOVING, bridge);
mutex_lock(&bridge_lock);
- list_del_init(&bridge->list);
+ list_move_tail(&bridge->list, &bridge_removed_list);
mutex_unlock(&bridge_lock);
mutex_destroy(&bridge->hpd_mutex);
--
2.50.1
