[PATCH v2 1/5] dt-bindings: connector: add GE SUNH hotplug addon connector

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

Add bindings for the GE SUNH add-on connector. This is a physical,
hot-pluggable connector that allows to attach and detach at runtime an
add-on adding peripherals on non-discoverable busses.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

---

NOTE: the second and third examples fail 'make dt_binding_check' because
      they are example of DT overlay code -- I'm not aware of a way to
      validate overlay examples as of now

This patch is new in v2.
---
 .../connector/ge,sunh-addon-connector.yaml         | 197 +++++++++++++++++++++
 MAINTAINERS                                        |   5 +
 2 files changed, 202 insertions(+)

diff --git a/Documentation/devicetree/bindings/connector/ge,sunh-addon-connector.yaml b/Documentation/devicetree/bindings/connector/ge,sunh-addon-connector.yaml
new file mode 100644
index 000000000000..c7ac62e5f2c9
--- /dev/null
+++ b/Documentation/devicetree/bindings/connector/ge,sunh-addon-connector.yaml
@@ -0,0 +1,197 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/connector/ge,sunh-addon-connector.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: GE SUNH hotplug add-on connector
+
+maintainers:
+  - Luca Ceresoli <luca.ceresoli@bootlin.com>
+
+description:
+  Represent the physical connector present on GE SUNH devices that allows
+  to attach and detach at runtime an add-on adding peripherals on
+  non-discoverable busses.
+
+  This connector has status GPIOs to notify the connection status to the
+  CPU and a reset GPIO to allow the CPU to reset all the peripherals on the
+  add-on. It also has a 4-lane MIPI DSI bus.
+
+  Add-on removal can happen at any moment under user control and without
+  prior notice to the CPU, making all of its components not usable
+  anymore. Later on, the same or a different add-on model can be connected.
+
+properties:
+  compatible:
+    const: ge,sunh-addon-connector
+
+  reset-gpios:
+    description: An output GPIO to reset the peripherals on the add-on.
+    maxItems: 1
+
+  plugged-gpios:
+    description: An input GPIO that is asserted if and only if an add-on is
+      physically connected.
+    maxItems: 1
+
+  powergood-gpios:
+    description: An input GPIO that is asserted if and only if power rails
+      on the add-on are stable.
+    maxItems: 1
+
+  ports:
+    $ref: /schemas/graph.yaml#/properties/ports
+
+    description: OF graph bindings modeling the MIPI DSI bus across the
+      connector. 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 any bridges and any other components up to the panel.
+
+    properties:
+      port@0:
+        $ref: /schemas/graph.yaml#/properties/port
+        description: The MIPI DSI bus line from the CPU to the connector.
+          The remote-endpoint sub-node must point to the last non-removable
+          component of the video pipeline.
+
+      port@1:
+        $ref: /schemas/graph.yaml#/properties/port
+
+        description: The MIPI DSI bus line from the connector to the
+          add-on. The remote-endpoint sub-node must point to the first
+          add-on component of the video pipeline. As it describes the
+          hot-pluggable hardware, the endpoint node cannot be filled until
+          an add-on is detected, so this needs to be done by a device tree
+          overlay at runtime.
+
+    required:
+      - port@0
+      - port@1
+
+required:
+  - compatible
+
+unevaluatedProperties: false
+
+examples:
+  # Main DTS describing the "main" board up to the connector
+  - |
+    / {
+        #include <dt-bindings/gpio/gpio.h>
+
+        addon_connector: addon-connector {
+            compatible = "ge,sunh-addon-connector";
+            reset-gpios = <&gpio1 1 GPIO_ACTIVE_LOW>;
+            plugged-gpios = <&gpio1 2 GPIO_ACTIVE_LOW>;
+            powergood-gpios = <&gpio1 3 GPIO_ACTIVE_HIGH>;
+
+            ports {
+                #address-cells = <1>;
+                #size-cells = <0>;
+
+                port@0 {
+                    reg = <0>;
+
+                    hotplug_conn_dsi_in: endpoint {
+                        remote-endpoint = <&previous_bridge_out>;
+                    };
+                };
+
+                port@1 {
+                    reg = <1>;
+
+                    hotplug_conn_dsi_out: endpoint {
+                        // remote-endpoint to be added by overlay
+                    };
+                };
+            };
+        };
+    };
+
+  # "base" overlay describing the common components on every add-on that
+  # are required to read the model ID
+  - |
+    &i2c1 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        eeprom@50 {
+            compatible = "atmel,24c64";
+            reg = <0x50>;
+
+            nvmem-layout {
+                compatible = "fixed-layout";
+                #address-cells = <1>;
+                #size-cells = <1>;
+
+                addon_model_id: addon-model-id@400 {
+                    reg = <0x400 0x1>;
+                };
+            };
+        };
+    };
+
+    &addon_connector {
+        nvmem-cells = <&addon_model_id>;
+        nvmem-cell-names = "id";
+    };
+
+  # Add-on-specific overlay describing all add-on components not in the
+  # "base" overlay
+  - |
+    &hotplug_conn_dsi_out {
+        remote-endpoint = <&addon_bridge_in>;
+    };
+
+    &i2c1 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        dsi-lvds-bridge@42 {
+            compatible = "some-video-bridge";
+            reg = <0x42>;
+
+            ports {
+                #address-cells = <1>;
+                #size-cells = <0>;
+
+                port@0 {
+                    reg = <0>;
+
+                    addon_bridge_in: endpoint {
+                        remote-endpoint = <&hotplug_conn_dsi_out>;
+                        data-lanes = <1 2 3 4>;
+                    };
+                };
+
+                port@1 {
+                    reg = <1>;
+
+                    addon_bridge_out: endpoint {
+                        remote-endpoint = <&panel_in>;
+                    };
+                };
+            };
+        };
+    };
+
+    &{/}
+    {
+    panel {
+        ports {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            port@0{
+                reg = <0>;
+
+                panel_in: endpoint {
+                    remote-endpoint = <&addon_bridge_out>;
+                };
+            };
+        };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index ec0284125e8f..4955501217eb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9897,6 +9897,11 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/iio/pressure/honeywell,mprls0025pa.yaml
 F:	drivers/iio/pressure/mprls0025pa*
 
+HOTPLUG CONNECTOR FOR GE SUNH ADDONS
+M:	Luca Ceresoli <luca.ceresoli@bootlin.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/connector/ge,sunh-addon-connector.yaml
+
 HP BIOSCFG DRIVER
 M:	Jorge Lopez <jorge.lopez2@hp.com>
 L:	platform-driver-x86@vger.kernel.org

-- 
2.34.1