linux-kernel - Re: [PATCH] Revert "drm/display: bridge_connector: get/put the stored bridges"

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Message-Id: <DDKQE4TIEXYJ.12G2WBT0R8UE4@bootlin.com>
Date: Fri, 17 Oct 2025 18:17:45 +0200
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Luca Ceresoli" <luca.ceresoli@...tlin.com>, "Marek Szyprowski"
 <m.szyprowski@...sung.com>, "Naresh Kamboju" <naresh.kamboju@...aro.org>,
 "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>, "Dmitry
 Baryshkov" <dmitry.baryshkov@....qualcomm.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] Revert "drm/display: bridge_connector: get/put the
 stored bridges"

Hello,

On Thu Oct 16, 2025 at 4:53 PM CEST, Luca Ceresoli wrote:
> This reverts commit 2be300f9a0b6f6b0ae2a90be97e558ec0535be54.
>
> The commit being reverted moved all the bridge_connector->bridge_*
> assignments to just before the final successful return in order to handle
> the bridge refcounting in a clean way.
>
> This introduced a bug, because a bit before the successful return
> drmm_connector_hdmi_cec_register() is called, which calls funcs->init()
> which is drm_bridge_connector_hdmi_cec_init() which needs
> bridge_connector->bridge_hdmi_cec to be set.
>
> The reported bug may be fixed in a relatively simple way, but other similar
> patterns are potentially present, so just revert the offending commit. A
> different approach will be implemented.
>
> Fixes: 2be300f9a0b6 ("drm/display: bridge_connector: get/put the stored bridges")
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Closes: https://lore.kernel.org/all/336fbfdd-c424-490e-b5d1-8ee84043dc80@samsung.com/
> Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
> Closes: https://lore.kernel.org/r/CA+G9fYuKHp3QgPKjgFY3TfkDdh5Vf=Ae5pCW+eU41Bu=D7th2g@mail.gmail.com
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

Please ignore this series. I have sent v2 with this exact same patch, plus
two patches re-adding the reverted feature without the same bug:

https://lore.kernel.org/lkml/20251017-drm-bridge-alloc-getput-bridge-connector-fix-hdmi_cec-v2-0-667abf6d47c0@bootlin.com/

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com