linux-kernel - Re: [PATCH 3/3] drm/bridge: imx8qxp-pixel-combiner: Fix bailout for imx8qxp_pc_bridge

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Message-Id: <DFYE5QDGOF28.2S7XJ1IFZIMX0@bootlin.com>
Date: Mon, 26 Jan 2026 09:51:49 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Liu Ying" <victor.liu@....com>, "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>, "Shawn Guo"
 <shawnguo@...nel.org>, "Sascha Hauer" <s.hauer@...gutronix.de>,
 "Pengutronix Kernel Team" <kernel@...gutronix.de>, "Fabio Estevam"
 <festevam@...il.com>
Cc: <dri-devel@...ts.freedesktop.org>, <imx@...ts.linux.dev>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] drm/bridge: imx8qxp-pixel-combiner: Fix bailout for
 imx8qxp_pc_bridge_probe()

On Mon Jan 26, 2026 at 9:47 AM CET, Liu Ying wrote:
>
>
> On Mon, Jan 26, 2026 at 09:33:38AM +0100, Luca Ceresoli wrote:
>> On Fri Jan 23, 2026 at 10:22 AM CET, Liu Ying wrote:
>>> In case the channel0 is unavailable and bailing out from free_child is
>>> needed when we fail to add a DRM bridge for the available channel1,
>>> pointer pc->ch[0] in the bailout path would be NULL and it would be
>>> dereferenced as pc->ch[0]->bridge.next_bridge.  Fix this by checking
>>> pc->ch[0] before dereferencing it.
>>
>> Thanks for checking this code and providing fixes! These drivers have a
>> complex code path so I had a hard time in following the logic without neing
>> able to test on hardware. Apologies for the issues emerged.
>
> Thanks for your quick review and hard work!
>
>>
>>> Fixes: ae754f049ce1 ("drm/bridge: imx8qxp-pixel-combiner: get/put the next bridge")
>>> Fixes: 99764593528f ("drm/bridge: imx8qxp-pixel-combiner: convert to devm_drm_bridge_alloc() API")
>>
>> The bug was introduced by 99764593528f, while ae754f049ce1 is not changing
>> the bug, so for the sake of precision we can remove the first 'Fixes:'
>> line.
>
> I added Fixes tag for ae754f049ce1 because it is the first commit which
> this commit could be applied upon properly.  Maybe this helps some tools
> apply this commit or maybe tools are smart enough to find ae754f049ce1
> automatically?

Uhm, good point, maybe it can be a useful reference for the stable team to
backport the fix... Well, let's leave both lines then:

Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

I'm applying this series perhaps tomorrow (if no one does it before).

Luca

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