[PATCH v2 0/9] drm/bridge: get/put the bridge when looping over the encoder chain

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

This series adds drm_bridge_get/put() calls for DRM bridges used when
looping over bridges in an encoder chain.

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 (in v6.16-rc1)
    B. ✔ convert all bridge drivers to new API (now in drm-misc-next)
    C. ✔ kunit tests (now in drm-misc-next)
    D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
         and warn on old allocation pattern (now in drm-misc-next)
    E. ➜ add get/put on drm_bridge accessors
       1. ✔ drm_bridge_chain_get_first_bridge() + add a cleanup action
       2. … drm_bridge_get_prev_bridge()
       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
 2. handle gracefully atomic updates during bridge removal
 3. … avoid DSI host drivers to have dangling pointers to DSI devices
 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)

Most loops on the encoder bridge chain are based on
drm_for_each_bridge_in_chain(), which does not get/put the bridge pointed
to by the loop iterator.

Add a scoped variant that ensures ta reference to the bridge pointed to by
the iterator is taken/released before/after every iteration (and when
breaking out of the loop). Using the scoped version, the bridge being
iterated on will always have a reference taken during the shole
iteration. This is similar to what for_each_child_of_node() and similar
for_each_* macros do.

All conversions are trivial except for drm_bridge_connector_init() which
needs some preliminary cleanups (patches 1-2).

omapdrm/omap_encoder.c is the only driver iterating over the encoder bridge
chain starting from a specific bridge, instead of iterating over the whole
list. For this use case, add a drm_for_each_bridge_in_chain_from() variant.

This series depends on:

 * commit 103578241512 ("drm/bridge-connector: Fix bridge in
   drm_connector_hdmi_audio_init()"), currently in drm-misc-fixes, not yet
   on drm-misc-next

[0] https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/0cc6aadd7fc1e629b715ea3d1ba537ef2da95eec
[1] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/t/#u

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Changes in v2:
- Prune series dependency list
- Clarify wording in cover letter and patch 3
- Link to v1: https://lore.kernel.org/r/20250723-drm-bridge-alloc-getput-for_each_bridge-v1-0-be8f4ae006e9@bootlin.com

---
Luca Ceresoli (9):
      drm/display: bridge-connector: use scope-specific variable for the bridge pointer
      drm/display: bridge-connector: remove unused variable assignment
      drm/bridge: add drm_for_each_bridge_in_chain_scoped()
      drm/display: bridge-connector: use drm_for_each_bridge_in_chain_scoped()
      drm/atomic: use drm_for_each_bridge_in_chain_scoped()
      drm/bridge: use drm_for_each_bridge_in_chain_scoped()
      drm/bridge: remove drm_for_each_bridge_in_chain()
      drm/bridge: add drm_for_each_bridge_in_chain_from()
      drm/omap: use drm_for_each_bridge_in_chain_from()

 .clang-format                                  |  2 +-
 drivers/gpu/drm/display/drm_bridge_connector.c | 13 +++----
 drivers/gpu/drm/drm_atomic.c                   |  3 +-
 drivers/gpu/drm/drm_bridge.c                   |  3 +-
 drivers/gpu/drm/omapdrm/omap_encoder.c         |  4 +-
 include/drm/drm_bridge.h                       | 52 ++++++++++++++++++++++++--
 6 files changed, 58 insertions(+), 19 deletions(-)
---
base-commit: d2b48f2b30f25997a1ae1ad0cefac68c25f8c330
change-id: 20250718-drm-bridge-alloc-getput-for_each_bridge-f141ae17b65a
prerequisite-message-id: <20250620011616.118-1-kernel@airkyi.com>
prerequisite-patch-id: ba5a6a15ea02bcee387db0e92ffb4cd0e1fbf816

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