Re: [PATCH 1/4] dt-bindings: display: bridge: add the Hot-plug MIPI DSI connector

From: Rob Herring <robh@kernel.org>
To: Luca Ceresoli <luca.ceresoli@bootlin.com>
Cc: "Andrzej Hajda" <andrzej.hajda@intel.com>,
	"Neil Armstrong" <neil.armstrong@linaro.org>,
	"Robert Foss" <rfoss@kernel.org>,
	"Laurent Pinchart" <Laurent.pinchart@ideasonboard.com>,
	"Jonas Karlman" <jonas@kwiboo.se>,
	"Jernej Skrabec" <jernej.skrabec@gmail.com>,
	"David Airlie" <airlied@gmail.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Paul Kocialkowski" <contact@paulk.fr>,
	"Hervé Codina" <herve.codina@bootlin.com>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	"Paul Kocialkowski" <paul.kocialkowski@bootlin.com>
Subject: Re: [PATCH 1/4] dt-bindings: display: bridge: add the Hot-plug MIPI DSI connector
Date: Wed, 27 Mar 2024 11:09:08 -0500	[thread overview]
Message-ID: <20240327160908.GA3460963-robh@kernel.org> (raw)
In-Reply-To: <20240326-hotplug-drm-bridge-v1-1-4b51b5eb75d5@bootlin.com>

On Tue, Mar 26, 2024 at 05:28:11PM +0100, Luca Ceresoli wrote:
> Add bindings for a physical, hot-pluggable connector allowing the far end
> of a MIPI DSI bus to be connected and disconnected at runtime.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> ---
>  .../bridge/hotplug-video-connector-dsi.yaml        | 87 ++++++++++++++++++++++
>  MAINTAINERS                                        |  5 ++
>  2 files changed, 92 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/bridge/hotplug-video-connector-dsi.yaml b/Documentation/devicetree/bindings/display/bridge/hotplug-video-connector-dsi.yaml
> new file mode 100644
> index 000000000000..05beb8aa9ab4
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/hotplug-video-connector-dsi.yaml
> @@ -0,0 +1,87 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/bridge/hotplug-video-connector-dsi.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Hot-pluggable connector on a MIPI DSI bus
> +
> +maintainers:
> +  - Luca Ceresoli <luca.ceresoli@bootlin.com>
> +
> +description:
> +  A bridge representing a physical, hot-pluggable connector on a MIPI DSI
> +  video bus. The connector splits the video pipeline in a fixed part and a
> +  removable part.
> +
> +  The fixed part of the video pipeline includes all components up to the
> +  display controller and 0 or more bridges. The removable part includes one
> +  or more bridges and any other components up to the panel.
> +
> +  The removable part of the pipeline can be physically disconnected at any
> +  moment, making all of its components not usable anymore. The same or a
> +  different removable part of the pipeline can be reconnected later on.
> +
> +  Note that the hotplug-video-connector does not describe video busses
> +  having native hotplug capabilities in the hardware, such as HDMI.
> +
> +properties:
> +  compatible:
> +    const: hotplug-video-connector-dsi

Got a spec for this connector? How do I know if I have one or not?

The problem here is what else is on this connector? GPIO controls, 
power rails, etc.?

If this is some kind of standard connector, then we need to be able to 
remap everything on the connector not just DSI signals. And for that, 
it's not just DSI signals, so I'd say we would need some sort of generic 
graph remapping that the core graph code handles transparently.

 If it is not standard, then you don't need any remapping and can just 
use an overlay that connects the ports directly.

Rob