Message-Id: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-0-bad7eba5d117@bootlin.com>
Date: Fri, 20 Jun 2025 11:32:05 +0200
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>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, 
 Anusha Srivatsa <asrivats@...hat.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 reference in
 drm_bridge.c, warn on old alloc pattern

This small series adds drm_bridge_get/put() calls where applicable in the
bridge core code, and adds a warning when the old allocation patter is
used.

This is part of the work towards removal of bridges from a still existing
DRM pipeline without use-after-free.

The steps in the grand plan [1] are:

 1. ➜ add refcounting to DRM bridges (struct drm_bridge)
 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)

This series is part of step 1 of the grand plan.

Current tasks in step 1 of the grand plan:

 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. ➜ after (B), add get/put to drm_bridge_add/remove() + attach/detech()
      and warn on old allocation pattern (this series)
 E. after (B), convert accessors; this is a large work and can be done
    in chunks
 F. debugfs improvements

Specifically, this series does two things related to the recently
introduced devm_drm_bridge_alloc() [0]:

 A) add drm_bridge_get/put() in the two places within drm_bridge.c where a
    bridge reference is taken/relased
 B) add a warning on bridges using the old allocation pattern instead of
    devm_drm_bridge_alloc()

These are loosely related topics, but I'm sending them in a single series
to avoid trivial patch conflicts, as they touch the same lines. This will
holefully help getting the patches applied more efficiently and quickly. I
hope this is fine being 3 small patches.

Part A) is made of patches 1 and 2. Those have been previously sent in
"[PATCH v7 00/11] drm/bridge: add devm_drm_bridge_alloc() with bridge
refcount" [2] (as patches 3 and 4), and already Reviewed-by Maxime at that
time. However they could not be applied until the conversion of all bridge
drivers to devm_drm_bridge_alloc(), which got completed a few days
ago. Hence the reason this is v8.

[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
[2] https://lore.kernel.org/all/20250314-drm-bridge-refcount-v7-0-152571f8c694@bootlin.com/

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
Luca Ceresoli (3):
      drm/bridge: get/put the bridge reference in drm_bridge_add/remove()
      drm/bridge: get/put the bridge reference in drm_bridge_attach/detach()
      drm/bridge: add warning for bridges not using devm_drm_bridge_alloc()

 drivers/gpu/drm/drm_bridge.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)
---
base-commit: a59a271769149f0b8258507276f3d2a24370cbdb
change-id: 20250620-drm-bridge-alloc-getput-drm-bridge-c-0ab2ca481c37

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

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