dt-bindings: mailbox: mediatek,mt8196-vcp-mbox: add mtk vcp-mbox document

The MTK VCP mailbox enables the SoC to communicate with the VCP by passing
messages through 64 32-bit wide registers. It has 32 interrupt vectors in
either direction for signalling purposes.

This adds a binding for Mediatek VCP mailbox.

Signed-off-by: Jjian Zhou <jjian.zhou@mediatek.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

Documentation/devicetree/bindings/mailbox/mediatek,mt8196-vcp-mbox.yaml

@@ -0,0 +1,49 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/mediatek,mt8196-vcp-mbox.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek Video Companion Processor (VCP) mailbox
+
+maintainers:
+  - Jjian Zhou <Jjian.Zhou@mediatek.com>
+
+description:
+  The MTK VCP mailbox enables the SoC to communicate with the VCP by passing
+  messages through 64 32-bit wide registers. It has 32 interrupt vectors in
+  either direction for signalling purposes.
+
+properties:
+  compatible:
+    enum:
+      - mediatek,mt8196-vcp-mbox
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  "#mbox-cells":
+    const: 0
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - "#mbox-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+
+    mailbox@31b80000 {
+        compatible = "mediatek,mt8196-vcp-mbox";
+        reg = <0x31b80000 0x1000>;
+        interrupts = <GIC_SPI 789 IRQ_TYPE_LEVEL_HIGH 0>;
+        #mbox-cells = <0>;
+    };