linux-kernel - [PATCH 0/3] drm/bridge: get/put the bridge returned by drm_bridge_get_prev

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Message-Id: <20250709-drm-bridge-alloc-getput-drm_bridge_get_prev_bridge-v1-0-34ba6f395aaa@bootlin.com>
Date: Wed, 09 Jul 2025 17:59:36 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH 0/3] drm/bridge: get/put the bridge returned by
 drm_bridge_get_prev_bridge()

This series adds drm_bridge_get/put() calls for DRM bridges returned by
drm_bridge_get_prev_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_chain_get_last_bridge()
       3. ➜ drm_bridge_get_prev_bridge()
       4. drm_bridge_get_next_bridge()
       5. drm_for_each_bridge_in_chain()
       6. drm_bridge_connector_init
       7. of_drm_find_bridge
       8. 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)

[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@...tlin.com>
---
Luca Ceresoli (3):
      drm/bridge: get the bridge returned by drm_bridge_get_prev_bridge()
      drm/bridge: select_bus_fmt_recursive(): put the bridge obtained by drm_bridge_get_prev_bridge()
      drm/bridge: display-connector: put the bridge obtained by drm_bridge_get_prev_bridge()

 drivers/gpu/drm/bridge/display-connector.c | 4 ++--
 drivers/gpu/drm/drm_bridge.c               | 4 ++--
 include/drm/drm_bridge.h                   | 9 ++++++++-
 3 files changed, 12 insertions(+), 5 deletions(-)
---
base-commit: 0f168e7be696a17487e83d1d47e5a408a181080f
change-id: 20250709-drm-bridge-alloc-getput-drm_bridge_get_prev_bridge-9470dca81bb3

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