dt-bindings: mediatek,dp: Add Display Port binding

This controller is present on several mediatek hardware. Currently
mt8195 and mt8395 have this controller without a functional difference,
so only one compatible field is added.

The controller can have two forms, as a normal display port and as an
embedded display port.
Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220901044149.16782-2-rex-bc.chen@mediatek.com

Documentation/devicetree/bindings/display/mediatek/mediatek,dp.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/mediatek/mediatek,dp.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek Display Port Controller
+
+maintainers:
+  - Chun-Kuang Hu <chunkuang.hu@kernel.org>
+  - Jitao shi <jitao.shi@mediatek.com>
+
+description: |
+  MediaTek DP and eDP are different hardwares and there are some features
+  which are not supported for eDP. For example, audio is not supported for
+  eDP. Therefore, we need to use two different compatibles to describe them.
+  In addition, We just need to enable the power domain of DP, so the clock
+  of DP is generated by itself and we are not using other PLL to generate
+  clocks.
+
+properties:
+  compatible:
+    enum:
+      - mediatek,mt8195-dp-tx
+      - mediatek,mt8195-edp-tx
+
+  reg:
+    maxItems: 1
+
+  nvmem-cells:
+    maxItems: 1
+    description: efuse data for display port calibration
+
+  nvmem-cell-names:
+    const: dp_calibration_data
+
+  power-domains:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  ports:
+    $ref: /schemas/graph.yaml#/properties/ports
+    properties:
+      port@0:
+        $ref: /schemas/graph.yaml#/properties/port
+        description: Input endpoint of the controller, usually dp_intf
+
+      port@1:
+        $ref: /schemas/graph.yaml#/$defs/port-base
+        unevaluatedProperties: false
+        description: Output endpoint of the controller
+        properties:
+          endpoint:
+            $ref: /schemas/media/video-interfaces.yaml#
+            unevaluatedProperties: false
+            properties:
+              data-lanes:
+                description: |
+                  number of lanes supported by the hardware.
+                  The possible values:
+                  0       - For 1 lane enabled in IP.
+                  0 1     - For 2 lanes enabled in IP.
+                  0 1 2 3 - For 4 lanes enabled in IP.
+                minItems: 1
+                maxItems: 4
+            required:
+              - data-lanes
+
+    required:
+      - port@0
+      - port@1
+
+  max-linkrate-mhz:
+    enum: [ 1620, 2700, 5400, 8100 ]
+    description: maximum link rate supported by the hardware.
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - ports
+  - max-linkrate-mhz
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/power/mt8195-power.h>
+    dptx@1c600000 {
+        compatible = "mediatek,mt8195-dp-tx";
+        reg = <0x1c600000 0x8000>;
+        power-domains = <&spm MT8195_POWER_DOMAIN_DP_TX>;
+        interrupts = <GIC_SPI 458 IRQ_TYPE_LEVEL_HIGH 0>;
+        max-linkrate-mhz = <8100>;
+
+        ports {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            port@0 {
+                reg = <0>;
+                dptx_in: endpoint {
+                    remote-endpoint = <&dp_intf0_out>;
+                };
+            };
+            port@1 {
+                reg = <1>;
+                dptx_out: endpoint {
+                    data-lanes = <0 1 2 3>;
+                };
+            };
+        };
+    };