linux-kernel - Re: [PATCH 0/4] drm/bridge: enforce drm_bridge_add() before drm_bridge

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Message-ID: <f3904ae1-bf1b-455f-b5ba-5d625b76222f@gmail.com>
Date: Sat, 18 Oct 2025 14:49:27 +0200
From: Raphaël Gallais-Pou <rgallaispou@...il.com>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Alain Volmat <alain.volmat@...s.st.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>,
 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>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] drm/bridge: enforce drm_bridge_add() before
 drm_bridge_attach()



Le 03/10/2025 à 10:59, Luca Ceresoli a écrit :
> This small series enforces that DRM bridges must be added before they are
> attached as discussed in [1].
> 
> 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 [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() [0])
>      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 a cleanup action
>              (drm-misc-next)
>         2. ✔ drm_bridge_get_prev_bridge() (drm-misc-next)
>         3. ✔ drm_bridge_get_next_bridge() (drm-misc-next)
>         4. ✔ drm_for_each_bridge_in_chain() (drm-misc-next)
>         5. ✔ drm_bridge_connector_init (drm-misc-next)
>         6. … protect encoder bridge chain with a mutex
>         7. of_drm_find_bridge
>         8. drm_of_find_panel_or_bridge, *_of_get_bridge
>         9. ➜ enforce drm_bridge_add before drm_bridge_attach
>      F. ✔ debugfs improvements
>         1. ✔ add top-level 'bridges' file (v6.16)
>         2. ✔ show refcount and list removed bridges (drm-misc-next)
>   2. … handle gracefully atomic updates during bridge removal
>   3. … DSI host-device driver interaction
>   4. ✔ removing the need for the "always-disconnected" connector
>   5. finish the hotplug bridge work, moving code to the core and potentially
>      removing the hotplug-bridge itself (this needs to be clarified as
>      points 1-3 are developed)
> 
> Series layout:
>   - patches 1-2: add missing drm_bridge_add() to the 2 drivers known for not
>                  calling it
>   - patch 3: document that drm_bridge_add() is required before attach
>   - patch 4: add a warning in drm_bridge_attach() is drm_bridge_add() was
>              not called
> 
> The added warning might reveal more non-compliant drivers, in that case
> they will be fixed as they are found.
> 
> [0] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/#t
> [1] https://lore.kernel.org/all/20250709-sophisticated-loon-of-rain-6ccdd8@houat/
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> ---
> Luca Ceresoli (4):
>        drm/sti: hda: add bridge before attaching
>        drm/sti: hdmi: add bridge before attaching
>        drm/bridge: document that adding a bridge is mandatory before attach
>        drm/bridge: add warning for bridges attached without being added
> 
>   drivers/gpu/drm/drm_bridge.c   | 6 ++++++
>   drivers/gpu/drm/sti/sti_hda.c  | 5 +++++
>   drivers/gpu/drm/sti/sti_hdmi.c | 2 ++
>   3 files changed, 13 insertions(+)
> ---
> base-commit: 0f2efbe6d8305b91c9b2c92ebaf8c24a614bc305
> change-id: 20251003-b4-drm-bridge-alloc-add-before-attach-ef312c0b8a8c
> 

If drm-misc maintainers agree I can merge the whole series.

Regards,
Raphaël> Best regards,