Re: [PATCH 1/4] dt-bindings: display: bridge: add the Hot-plug MIPI DSI connector
Hello Rob,
[+Cc Wolfram for the I2C discussion below]
thanks for your feedback.
On Wed, 27 Mar 2024 11:09:08 -0500
Rob Herring wrote:
> 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
> > ---
> > .../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 ..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
> > +
> > +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.
This is not a standardized connector. And it couldn't be: to the best of
my knowledge no standard removable MIPI DSI connector exists at all.
This whole work is unavoidably breaking some long-standing assumptions
and opening some new challenges: giving a proper DT description to
runtime-pluggable hardware and breaking the dogma that a DRM pipeline
is not removable, to name some. So I think it's better to take a step
back and describe the big picture.
As mentioned in the cover letter ("Development roadmap" section),
together with Hervé we are working on a set of patches to allow this
sort of removable hardware to be handled properly by the Linux kernel.
From the cover letter:
> The use case we are working on is to support professional products that
> have a portable "main" part running on battery, with the main SoC and able
> to work autonomously with limited features, and that can be connected to an
> "add-on" part that is not portable and adds more features.
The add-on gets connected via a connector that is not standardized.
There is a well-defined part number for the mechanical connector, but
the pin usage is custom for the product. Connector pins include:
* I2C lines to access various chips on the add-on
- one of these chips is an EEPROM with the add-on product ID
* Some pins to report to the CPU whether the add-on is connected and
add-on power rails are stable (these are wired to SoC GPIOs)
* An interrupt line collecting IRQs from the add-on chips
* MIPI DSI to drive a panel on the add-on
* Gigabit Ethernet (4 pairs)
* USB lines
* A few more accessory pins
Some of these are not problematic: USB is hot-pluggable and
auto-discoverable by nature, Ethernet pins are just connected directly
to the RJ-45 connector so the add-on acts as an Ethernet or USB cable.
For everything else there is going to be a separate patch series
with code to detect add-on connection, read the ID, identify the
appropriate DT overlay and load it, and unload it on disconnection.
Before that, it's good to discuss how the device tree should describe
the whole hardware described above, in these terms:
1. Should device tree
Re: [PATCH 1/4] dt-bindings: display: bridge: add the Hot-plug MIPI DSI connector
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 > --- > .../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 ..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 > + > +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
[PATCH 1/4] dt-bindings: display: bridge: add the Hot-plug MIPI DSI connector
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
---
.../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 ..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
+
+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
+
+ ports:
+$ref: /schemas/graph.yaml#/properties/ports
+
+properties:
+ port@0:
+$ref: /schemas/graph.yaml#/properties/port
+description:
+ The end of the fixed part of the MIPI DSI bus (terminating at the
+ hotplug connector). The remote-endpoint sub-node must point to
+ the previous component of the video pipeline.
+
+ port@1:
+$ref: /schemas/graph.yaml#/properties/port
+description:
+ The start of the removable part of the MIPI DSI bus (starting
+ from the hotplug connector). The remote-endpoint sub-node must
+ point to the next component of the video pipeline.
+
+required:
+ - port@0
+ - port@1
+
+required:
+ - compatible
+ - ports
+
+additionalProperties: false
+
+examples:
+ - |
+hotplug-video-connector {
+compatible = "hotplug-video-connector-dsi";
+
+ports {
+#address-cells = <1>;
+#size-cells = <0>;
+
+port@0 {
+reg = <0>;
+
+hotplug_connector_in: endpoint {
+remote-endpoint = <&previous_bridge_out>;
+};
+};
+
+port@1 {
+reg = <1>;
+
+hotplug_connector_out: endpoint {
+remote-endpoint = <&next_bridge_in>;
+};
+};
+};
+};
+
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index aa3b947fb080..e1affd13e30b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6716,6 +6716,11 @@ T: git git://anongit.freedesktop.org/drm/drm-misc
F: Documentation/devicetree/bindings/display/panel/himax,hx8394.yaml
F: drivers/gpu/drm/panel/panel-himax-hx8394.c
+DRM DRIVER FOR HOTPLUG VIDEO CONNECTOR BRIDGE
+M: Luca Ceresoli
+S: Maintained
+F:
Documentation/devicetree/bindings/display/bridge/hotplug-video-connector-dsi.yaml
+
DRM DRIVER FOR HX8357D PANELS
S: Orphan
T: git git://anongit.freedesktop.org/drm/drm-misc
--
2.34.1
