[PATCH v3 00/22] drm/bridge: add of_drm_find_and_get_bridge() and a managed *next_bridge, deprecate of_drm_find_bridge()

Luca Ceresoli
2025-12-16T17:59:34Z

This series deprecates of_drm_find_bridge(), adds a replacement which
handles bridge refcounting, and converts some of the direct users.

This is part of the work to support hotplug of DRM bridges. 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()
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()
a. ➜ add of_drm_find_and_get_bridge(), convert some direct users
b. convert other direct users
c. convert bridge-only drm_of_find_panel_or_bridge() users
8. drm_of_find_panel_or_bridge, *_of_get_bridge
9. ✔ enforce drm_bridge_add before drm_bridge_attach (v6.19)
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 (v6.20?)
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)

[0] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/#t

Almost all the functions returning a struct drm_bridge pointer have been
modified to drm_bridge_get() the returned bridge, and their users updated
to drm_bridge_put() it. See items 1.E.{1-6} above.

of_drm_find_bridge() could be modified easily in the same way, but it has a
lot of (direct + indirect) callers, and most notably
drm_of_find_panel_or_bridge() which is very hard to adapt without reworking
the panel_bridge lifetime.

This has been discussed in [1] and Maxime proposed an incremental approach:

> So maybe we can just create drm_of_find_bridge() that takes a reference,
> make of_drm_find_bridge() deprecated in favour of drm_of_find_bridge(),
> add a TODO, and call it a day. People will gradually switch to the new
> API over time.

That proposal is implemented by this series with the various changes
discussed after the initial proposal. Some of the direct callers are also
converted: a few of the simple ones plus two complex cases. One of the
complex cases also shows how to use the .destroy func when the next_bridge
is not enough.

Follow-up series will:
- convert remaining direct callers of of_drm_find_bridge()
- convert simple cases of drm_of_find_panel_or_bridge()

[1] https://lore.kernel.org/dri-devel/20250319-stylish-lime-mongoose-0a18ad@houat/

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Changes in v3:
- Completely rewrote using the __drm_bridge_free() idea to prevent
use-after-free of the next_bridge for the common cases
- Added needed cleanups to the imx8qxp-pixel-link and imx8qxp-pxl2dpi
drivers
- Removed various patches converting simple cases, to reduce the number of
e-mails sent; will be moved to the follow-up series
- Link to v2: https://lore.kernel.org/r/20251128-drm-bridge-alloc-getput-drm_of_find_bridge-v2-0-88f8a107eca2@bootlin.com

Changes in v2:
- All patches: renamed drm_of_find_bridge() -> of_drm_get_bridge()
- Various fixes and improvements to patches 1-6, see individual patches
changelog
- Removed bouncing recipient: Edmund Dea <edmund.j.dea@intel.com>
- Link to v1: https://lore.kernel.org/r/20251119-drm-bridge-alloc-getput-drm_of_find_bridge-v1-0-0db98a7fe474@bootlin.com

---
Luca Ceresoli (22):
drm/bridge: add of_drm_find_and_get_bridge()
drm/bridge: deprecate of_drm_find_bridge()
drm/todo: add entry about converting to of_drm_find_and_get_bridge()
drm/bridge: make of_drm_find_bridge() a wrapper of of_drm_find_and_get_bridge()
drm/arcpgu: convert to of_drm_find_and_get_bridge()
drm/bridge: add next_bridge pointer to struct drm_bridge
drm/bridge: ite-it66121: get/put the next bridge
drm/bridge: imx8qxp-pixel-combiner: get/put the next bridge
drm/bridge: simple-bridge: get/put the next bridge
drm/meson: encoder_cvbs: get/put the next bridge
drm/meson: encoder_dsi: get/put the next bridge
drm/meson: encoder_hdmi: get/put the next bridge
drm/bridge: imx8qxp-pxl2dpi: simplify put of device_node pointers
drm/bridge: imx8qxp-pxl2dpi: remove excess error message
drm/bridge: imx8qxp-pxl2dpi: imx8qxp_pxl2dpi_find_next_bridge: return int, not ERR_PTR
drm/bridge: imx8qxp-pxl2dpi: get/put the next bridge
drm/bridge: imx8qxp-pxl2dpi: get/put the companion bridge
drm/bridge: imx8qxp-pixel-link: simplify logic to find next bridge
drm/bridge: imx8qxp-pixel-link: simplify freeing of the remote device_node
drm/bridge: imx8qxp-pixel-link: remove excess error message
drm/bridge: imx8qxp-pixel-link: imx8qxp_pixel_link_find_next_bridge: return int, not ERR_PTR
drm/bridge: imx8qxp-pixel-link: get/put the next bridge

Documentation/gpu/todo.rst | 16 +++++
.../gpu/drm/bridge/imx/imx8qxp-pixel-combiner.c | 9 ++-
drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 56 ++++++++----------
drivers/gpu/drm/bridge/imx/imx8qxp-pxl2dpi.c | 63 ++++++++------------
drivers/gpu/drm/bridge/ite-it66121.c | 7 +--
drivers/gpu/drm/bridge/simple-bridge.c | 15 +++--
drivers/gpu/drm/drm_bridge.c | 69 +++++++++++++++++-----
drivers/gpu/drm/meson/meson_encoder_cvbs.c | 7 +--
drivers/gpu/drm/meson/meson_encoder_dsi.c | 7 +--
drivers/gpu/drm/meson/meson_encoder_hdmi.c | 9 ++-
drivers/gpu/drm/tiny/arcpgu.c | 5 +-
include/drm/drm_bridge.h | 16 +++++
12 files changed, 162 insertions(+), 117 deletions(-)
---
base-commit: 441223656cd43291f4f8277ab98fd3e9e61eeb33
change-id: 20251117-drm-bridge-alloc-getput-drm_of_find_bridge-74903367448d

Best regards,
--
Luca Ceresoli <luca.ceresoli@bootlin.com>