drm/panel: Add DT bindings for Samsung LMS397KF04

This adds device tree bindings for the Samsung LMS397KF04
RGB DPI display panel.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210405234713.3190693-1-linus.walleij@linaro.org

Documentation/devicetree/bindings/display/panel/samsung,lms397kf04.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/samsung,lms397kf04.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Samsung LMS397KF04 display panel
+
+description: The datasheet claims this is based around a display controller
+  named DB7430 with a separate backlight controller.
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+allOf:
+  - $ref: panel-common.yaml#
+
+properties:
+  compatible:
+    const: samsung,lms397kf04
+
+  reg: true
+
+  reset-gpios: true
+
+  vci-supply:
+    description: regulator that supplies the VCI analog voltage
+      usually around 3.0 V
+
+  vccio-supply:
+    description: regulator that supplies the VCCIO voltage usually
+      around 1.8 V
+
+  backlight: true
+
+  spi-max-frequency:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: inherited as a SPI client node, the datasheet specifies
+      maximum 300 ns minimum cycle which gives around 3 MHz max frequency
+    maximum: 3000000
+
+  port: true
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    spi {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      panel@0 {
+        compatible = "samsung,lms397kf04";
+        spi-max-frequency = <3000000>;
+        reg = <0>;
+        vci-supply = <&lcd_3v0_reg>;
+        vccio-supply = <&lcd_1v8_reg>;
+        reset-gpios = <&gpio 1 GPIO_ACTIVE_LOW>;
+        backlight = <&ktd259>;
+
+        port {
+          panel_in: endpoint {
+            remote-endpoint = <&display_out>;
+          };
+        };
+      };
+    };
+
+...