This small series enforces that DRM bridges must be added before they are
attached as discussed in [1].
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 [0].
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)
C. ✔ kunit tests (v6.17)
D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
and warn on old allocation pattern (v6.17)
E. ➜ add get/put on drm_bridge accessors
1. ✔ drm_bridge_chain_get_first_bridge(), add cleanup action (v6.18)
2. ✔ drm_bridge_get_prev_bridge() (v6.18)
3. ✔ drm_bridge_get_next_bridge() (v6.19)
4. ✔ drm_for_each_bridge_in_chain() (v6.19)
5. ✔ drm_bridge_connector_init (v6.19)
6. … protect encoder bridge chain with a mutex
7. of_drm_find_bridge
8. drm_of_find_panel_or_bridge, *_of_get_bridge
9. ➜ enforce drm_bridge_add before drm_bridge_attach
F. ✔ debugfs improvements
1. ✔ add top-level 'bridges' file (v6.16)
2. ✔ show refcount and list lingering bridges (v6.19)
2. … handle gracefully atomic updates during bridge removal
A. … Add drm_dev_enter/exit() to protect device resources
B. … protect private_obj removal from list
3. … DSI host-device driver interaction
4. ✔ removing the need for the "always-disconnected" connector
5. finish the hotplug bridge work, moving code to the core and potentially
removing the hotplug-bridge itself (this needs to be clarified as
points 1-3 are developed)
Series layout:
- patches 1-2: add missing drm_bridge_add() to the 2 drivers known for not
calling it
- patch 3: document that drm_bridge_add() is required before attach
- patch 4: add a warning in drm_bridge_attach() is drm_bridge_add() was
not called
- patch 5: add a warning for bridges missing both devm_drm_bridge_alloc()
and drm_bridge_add()
The added warning might reveal more non-compliant drivers, in that case
they will be fixed as they are found.
[0] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/#t
[1] https://lore.kernel.org/all/20250709-sophisticated-loon-of-rain-6ccdd8@houat/
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Changes in v3:
- Searched for any remaining drivers not calling drm_bridge_add(); found 1,
added patch 6 to convert it
- Added Suggested-by which was missing in patch 4, removed misplaced Link: tags
- Added review tags to patches 1-2
- Link to v2: https://lore.kernel.org/r/20251021-b4-drm-bridge-alloc-add-before-attach-v2-0-c17cc1bbff72@bootlin.com
Changes in v2:
- Added patch 5
- Added review tags to patches 1-4 (patches unchanged)
- Link to v1: https://lore.kernel.org/r/20251003-b4-drm-bridge-alloc-add-before-attach-v1-0-92fb40d27704@bootlin.com
---
Luca Ceresoli (6):
drm/sti: hda: add bridge before attaching
drm/sti: hdmi: add bridge before attaching
drm/bridge: document that adding a bridge is mandatory before attach
drm/bridge: add warning for bridges attached without being added
drm/bridge: add warning for bridges using neither devm_drm_bridge_alloc() nor drm_bridge_add()
drm/bridge: synopsys: dw-dp: add bridge before attaching
drivers/gpu/drm/bridge/synopsys/dw-dp.c | 2 ++
drivers/gpu/drm/drm_bridge.c | 9 +++++++++
drivers/gpu/drm/sti/sti_hda.c | 5 +++++
drivers/gpu/drm/sti/sti_hdmi.c | 2 ++
4 files changed, 18 insertions(+)
---
base-commit: 761105adbbac91d00a9662e54de1c55513556a48
change-id: 20251003-b4-drm-bridge-alloc-add-before-attach-ef312c0b8a8c
Best regards,
--
Luca Ceresoli <luca.ceresoli@bootlin.com>