Documentation: bridge: Add documentation for ps8640 DT properties

Add documentation for DT properties supported by
ps8640 DSI-eDP converter.
Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Ulrich Hecht <uli@fpond.eu>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191230090419.137141-2-enric.balletbo@collabora.com

Documentation/devicetree/bindings/display/bridge/ps8640.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/bridge/ps8640.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MIPI DSI to eDP Video Format Converter Device Tree Bindings
+
+maintainers:
+  - Nicolas Boichat <drinkcat@chromium.org>
+  - Enric Balletbo i Serra <enric.balletbo@collabora.com>
+
+description: |
+  The PS8640 is a low power MIPI-to-eDP video format converter supporting
+  mobile devices with embedded panel resolutions up to 2048 x 1536. The
+  device accepts a single channel of MIPI DSI v1.1, with up to four lanes
+  plus clock, at a transmission rate up to 1.5Gbit/sec per lane. The
+  device outputs eDP v1.4, one or two lanes, at a link rate of up to
+  3.24Gbit/sec per lane.
+
+properties:
+  compatible:
+    const: parade,ps8640
+
+  reg:
+    maxItems: 1
+    description: Base I2C address of the device.
+
+  powerdown-gpios:
+    maxItems: 1
+    description: GPIO connected to active low powerdown.
+
+  reset-gpios:
+    maxItems: 1
+    description: GPIO connected to active low reset.
+
+  vdd12-supply:
+    maxItems: 1
+    description: Regulator for 1.2V digital core power.
+
+  vdd33-supply:
+    maxItems: 1
+    description: Regulator for 3.3V digital core power.
+
+  ports:
+    type: object
+    description:
+      A node containing DSI input & output port nodes with endpoint
+      definitions as documented in
+      Documentation/devicetree/bindings/media/video-interfaces.txt
+      Documentation/devicetree/bindings/graph.txt
+    properties:
+      port@0:
+        type: object
+        description: |
+          Video port for DSI input
+
+      port@1:
+        type: object
+        description: |
+          Video port for eDP output (panel or connector).
+
+    required:
+      - port@0
+
+required:
+  - compatible
+  - reg
+  - powerdown-gpios
+  - reset-gpios
+  - vdd12-supply
+  - vdd33-supply
+  - ports
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    i2c0 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        ps8640: edp-bridge@18 {
+            compatible = "parade,ps8640";
+            reg = <0x18>;
+            powerdown-gpios = <&pio 116 GPIO_ACTIVE_LOW>;
+            reset-gpios = <&pio 115 GPIO_ACTIVE_LOW>;
+            vdd12-supply = <&ps8640_fixed_1v2>;
+            vdd33-supply = <&mt6397_vgp2_reg>;
+
+            ports {
+                #address-cells = <1>;
+                #size-cells = <0>;
+
+                port@0 {
+                    reg = <0>;
+                    ps8640_in: endpoint {
+                        remote-endpoint = <&dsi0_out>;
+                    };
+                };
+
+                port@1 {
+                    reg = <1>;
+                    ps8640_out: endpoint {
+                        remote-endpoint = <&panel_in>;
+                   };
+                };
+            };
+        };
+    };
+