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

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Message-ID: <21f80397-be9c-49bd-b814-ea5f0eb5fdc8@bootlin.com>
Date: Thu, 11 Sep 2025 17:47:57 +0200
From: Miguel Gazquez <miguel.gazquez@...tlin.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Maxime Ripard <mripard@...nel.org>, 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 17:40, Miguel Gazquez a écrit :
> 
> 
> Le 11/09/2025 à 15:09, Dmitry Baryshkov a écrit :
>> On Thu, Sep 11, 2025 at 02:49:59PM +0200, Miguel Gazquez wrote:
>>>
>>>
>>> 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.
>>
>> How does it break devicetree? The drm_bridge_connector isn't a part of
>> DT.
> 
> 
> In the current situation, a board could have the tilcdc linked with a 
> bridge that does not support DRM_BRIDGE_ATTACH_NO_CONNECTOR (for 
> example, the analogix-anx6345) , and everything will work fine.
> If we convert the tilcdc to always use DRM_BRIDGE_ATTACH_NO_CONNECTOR, 
> that same configuration will stop working.
> 
> When I said "breaking devicetree" I meant that a devicetree describing 
> this setup would no longer produce a working system, not that the DT 
> files or bindings themselves are incorrect.
> I didn't find any upstream dts with this configuration, but maybe there 
> is some out-of-tree dts which would be affected.
> As far as I understand, we should avoid that.
> 

If I can rephrase myself, is my understanding correct ? Do we care about 
breaking out-of-tree dts ?

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