linux-kernel - Re: [PATCH] drm/bridge: ite-it66121: Add drm

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Message-ID: <012046ab-d866-4b3a-8c8a-e130bc2b9628@bootlin.com>
Date: Thu, 11 Sep 2025 14:49:59 +0200
From: Miguel Gazquez <miguel.gazquez@...tlin.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Phong LE <ple@...libre.com>, Neil Armstrong <neil.armstrong@...aro.org>,
 Andrzej Hajda <andrzej.hajda@...el.com>, 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>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
 miquel.raynal@...tlin.com, kory.maincent@...tlin.com,
 romain.gantois@...tlin.com, praneeth@...com,
 Aradhya Bhatia <a-bhatia1@...com>
Subject: Re: [PATCH] drm/bridge: ite-it66121: Add drm_connector support



Le 11/09/2025 à 11:50, Maxime Ripard a écrit :
> On Thu, Sep 11, 2025 at 10:51:06AM +0200, Miguel Gazquez wrote:
>>
>>
>> Le 10/09/2025 à 04:28, Dmitry Baryshkov a écrit :
>>> On Tue, Sep 09, 2025 at 06:16:43PM +0200, Miguel Gazquez wrote:
>>>> From: Aradhya Bhatia <a-bhatia1@...com>
>>>>
>>>> Add support for DRM connector and make the driver support the older
>>>> format of attaching connectors onto the encoder->bridge->connector
>>>> chain.
>>>> This makes the driver compatible with display controller that only
>>>> supports the old format.
>>>>
>>>> [Miguel Gazquez: Rebased + made driver work with or without
>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR]
>>>
>>> What is the use case for not using DRM_BRIDGE_ATTACH_NO_CONNECTOR?
>>
>> Some display controller drivers (like the tilcdc) call drm_bridge_attach
>> without DRM_BRIDGE_ATTACH_NO_CONNECTOR, so the bridge must support both with
>> and without DRM_BRIDGE_ATTACH_NO_CONNECTOR to be compatible with all display
>> controllers.
> 
> I'd rather convert tilcdc to use DRM_BRIDGE_ATTACH_NO_CONNECTOR then.

The problem is that doing that break devicetrees using the tilcdc and a 
bridge who doesn't support DRM_BRIDGE_ATTACH_NO_CONNECTOR (there are 
multiple bridges that don't support DRM_BRIDGE_ATTACH_NO_CONNECTOR), and 
if my understanding is correct breaking devicetrees is not allowed.

> 
> Maxime

-- 
Miguel Gazquez, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com