This series shows removed bridges to the global <debugfs>/dri/bridges file,
and shows the bridge refcount. Removed bridges are bridges after
drm_bridges_remove() but before they are eventually freed on the last
drm_bridge_put().
This is part of the work towards removal of bridges from a still existing
DRM pipeline without use-after-free. The grand plan was discussed in [1].
Here's the work breakdown (➜ marks the current series):
1. ➜ add refcounting to DRM bridges (struct drm_bridge)
(based on devm_drm_bridge_alloc() [0])
A. ✔ add new alloc API and refcounting (v6.16)
B. ✔ convert all bridge drivers to new API (v6.17-rc1)
C. ✔ kunit tests (v6.17-rc1)
D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
and warn on old allocation pattern (v6.17-rc1)
E. … add get/put on drm_bridge accessors
1. ✔ drm_bridge_chain_get_first_bridge() + add a cleanup action
(drm-misc-next)
2. ✔ drm_bridge_get_prev_bridge() (drm-misc-next)
3. … drm_bridge_get_next_bridge()
4. … drm_for_each_bridge_in_chain()
5. drm_bridge_connector_init
6. of_drm_find_bridge
7. drm_of_find_panel_or_bridge, *_of_get_bridge
F. ➜ debugfs improvements
1. ✔ add top-level 'bridges' file (v6.16)
2. ➜ show refcount and list removed bridges
2. … handle gracefully atomic updates during bridge removal
3. … DSI host-device driver interaction
4. finish the hotplug bridge work, removing the "always-disconnected"
connector, moving code to the core and potentially removing the
hotplug-bridge itself (this needs to be clarified as points 1-3 are
developed)
To show the removed bridges we need to keep track of them, thus add a new
global list to store them between drm_bridge_remove() and the eventual
free. This is bit tricky in case a bridge is removed and then re-added
before being freed. This is handled in patch 2.
This series depends on one other series:
* [PATCH v2 0/9] drm/bridge: get/put the bridge when looping over the encoder
chain
Link:
https://lore.kernel.org/r/20250808-drm-bridge-alloc-getput-for_each_bridge-v2-0-edb6ee81e...@bootlin.com
Reason: it uses drm_for_each_bridge_in_chain_scoped()
[0]
https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/0cc6aadd7fc1e629b715ea3d1ba537ef2da95eec
[1]
https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3...@bootlin.com/t/#u
Signed-off-by: Luca Ceresoli <luca.ceres...@bootlin.com>
---
This series was initially part of v6 of this other series:
- Link to v6:
https://lore.kernel.org/dri-devel/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3...@bootlin.com/
---
Luca Ceresoli (3):
drm/debugfs: bridges_show: show refcount
drm/bridge: add list of removed refcounted bridges
drm/debugfs: show removed bridges
drivers/gpu/drm/drm_bridge.c | 47 +++++++++++++++++++++++++++++++++++++-------
1 file changed, 40 insertions(+), 7 deletions(-)
---
base-commit: c8cea4371e5eca30cda8660aabb337747dabc51d
change-id: 20250408-drm-bridge-debugfs-removed-2579f892e4b3
Best regards,
--
Luca Ceresoli <luca.ceres...@bootlin.com>
