Message-Id: <20260206-drm-bridge-atomic-vs-remove-clear_and_put-v1-0-6f1a7d03c45f@bootlin.com>
Date: Fri, 06 Feb 2026 15:27:54 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: 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>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Inki Dae <inki.dae@...sung.com>, Jagan Teki <jagan@...rulasolutions.com>, 
 Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>, Ian Ray <ian.ray@...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 0/2] drm/bridge: add drm_bridge_clear_and_put()

This small series introduces drm_bridge_clear_and_put(), to give a easy and
safe way to put a bridge reference and clear the pointer without leaving a
possible use-after-free window.

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_get_bridge(), convert basic direct users
	        (v6.20?, one driver still pending)
	  b. ✔ convert direct of_drm_get_bridge() users, part 2 (v6.20?)
	  c. ✔ convert direct of_drm_get_bridge() users, part 3 (v6.20?)
	  d. … convert direct of_drm_get_bridge() users, part 4
	  e.   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
    C. ➜ Add drm_bridge_clear_and_put()
 3. … DSI host-device driver interaction
 4. ✔ removing the need for the "always-disconnected" connector
 5.   DRM bridge hotplug
    A.   Bridge hotplug management in the DRM core
    B.   Device tree description 

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

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
Luca Ceresoli (2):
      drm/bridge: add drm_bridge_clear_and_put()
      drm/bridge: samsung-dsim: use drm_bridge_clear_and_put() to put the next bridge

 drivers/gpu/drm/bridge/samsung-dsim.c |  6 ++----
 drivers/gpu/drm/drm_bridge.c          | 34 ++++++++++++++++++++++++++++++++++
 include/drm/drm_bridge.h              |  1 +
 3 files changed, 37 insertions(+), 4 deletions(-)
---
base-commit: 8991256a0a2699415b5e19bdc8f9d86154543546
change-id: 20260206-drm-bridge-atomic-vs-remove-clear_and_put-a424c752a061

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

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