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

[Maxime Ripard <mripard@kernel.org>]

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On Thu, Sep 11, 2025 at 05:47:57PM +0200, Miguel Gazquez wrote:
> 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@ti.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 ?

There's only so much we can do, and we can't fix issues we can't know
about. So no.

Maxime

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