Re: [PATCH] drm/bridge: ite-it66121: Add drm_connector support

[Miguel Gazquez]

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@xxxxxx>
> > > > > > >
> > > > > > > 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