[PATCH 0/9] drm/bridge: get/put the bridge returned by drm_bridge_get_last_bridge()

[Luca Ceresoli]

This series adds drm_bridge_get/put() calls for DRM bridges returned by
drm_bridge_get_last_bridge().

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)

There are various users of drm_bridge_get_last_bridge() which cannot be
converted easily. Luckily they are not really looking for the next bridge,
but for something else, such as getting the last bridge in the encoder
chain or checking whether a bridge is the last in the encoder chain. So
introduce better functions for those users and use them instead of
drm_bridge_get_last_bridge(), making the code cleaner at the same time.

Finally add a drm_bridge_get() ti drm_bridge_get_next_bridge() and
drm_bridge_put() to the remaining, and legitimate, calls.

[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 at bootlin.com>
---
Luca Ceresoli (9):
      list: add list_last_entry_or_null()
      drm/bridge: add drm_bridge_chain_get_last_bridge()
      drm/bridge: imx93-mipi-dsi: use drm_bridge_chain_get_last_bridge()
      drm/omapdrm: use drm_bridge_chain_get_last_bridge()
      drm/bridge: add drm_bridge_is_last()
      drm/display: bridge_connector: use drm_bridge_is_last()
      drm/bridge: get the bridge returned by drm_bridge_get_next_bridge()
      drm/bridge: put the bridge returned by drm_bridge_get_next_bridge()
      drm/imx: parallel-display: put the bridge returned by drm_bridge_get_next_bridge()

 drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c    | 12 ++++------
 drivers/gpu/drm/display/drm_bridge_connector.c |  5 ++--
 drivers/gpu/drm/drm_bridge.c                   |  2 ++
 drivers/gpu/drm/imx/ipuv3/parallel-display.c   |  4 +++-
 drivers/gpu/drm/omapdrm/omap_drv.c             |  8 +++----
 include/drm/drm_bridge.h                       | 32 +++++++++++++++++++++++++-
 include/linux/list.h                           | 14 +++++++++++
 7 files changed, 61 insertions(+), 16 deletions(-)
---
base-commit: 0f168e7be696a17487e83d1d47e5a408a181080f
change-id: 20250709-drm-bridge-alloc-getput-drm_bridge_get_next_bridge-1df6aaf62136

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