dt-bindings: display: Add Himax HX8394 panel controller

Add device tree bindings for panels based on the Himax HX8394 controller,
such as the HannStar HSD060BHW4 720x1440 TFT LCD panel that is connected
through a MIPI-DSI video interface.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230102230733.3506624-2-javierm@redhat.com

Documentation/devicetree/bindings/display/panel/himax,hx8394.yaml

+# SPDX-License-Identifier: (GPL-2.0-only or BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/himax,hx8394.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Himax HX8394 MIPI-DSI LCD panel controller
+
+maintainers:
+  - Ondrej Jirman <megi@xff.cz>
+  - Javier Martinez Canillas <javierm@redhat.com>
+
+description:
+  Device tree bindings for panels based on the Himax HX8394 controller,
+  such as the HannStar HSD060BHW4 720x1440 TFT LCD panel connected with
+  a MIPI-DSI video interface.
+
+allOf:
+  - $ref: panel-common.yaml#
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - hannstar,hsd060bhw4
+      - const: himax,hx8394
+
+  reg: true
+
+  reset-gpios: true
+
+  backlight: true
+
+  port: true
+
+  vcc-supply:
+    description: Panel power supply
+
+  iovcc-supply:
+    description: I/O voltage supply
+
+required:
+  - compatible
+  - reg
+  - reset-gpios
+  - backlight
+  - port
+  - vcc-supply
+  - iovcc-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    dsi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        panel@0 {
+            compatible = "hannstar,hsd060bhw4", "himax,hx8394";
+            reg = <0>;
+            vcc-supply = <&reg_2v8_p>;
+            iovcc-supply = <&reg_1v8_p>;
+            reset-gpios = <&gpio3 13 GPIO_ACTIVE_LOW>;
+            backlight = <&backlight>;
+
+            port {
+                mipi_in_panel: endpoint {
+                    remote-endpoint = <&mipi_out_panel>;
+                };
+            };
+        };
+    };
+
+...