dt-bindings: mailbox: Add thead,th1520-mailbox bindings

Add bindings for the mailbox controller. This work is based on the vendor
kernel. [1]

Link: https://github.com/revyos/thead-kernel.git [1]

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml

@@ -0,0 +1,89 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/thead,th1520-mbox.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: T-head TH1520 Mailbox Controller
+
+description:
+  The T-head mailbox controller enables communication and coordination between
+  cores within the SoC by passing messages (e.g., data, status, and control)
+  through mailbox channels. It also allows one core to signal another processor
+  using interrupts via the Interrupt Controller Unit (ICU).
+
+maintainers:
+  - Michal Wilczynski <m.wilczynski@samsung.com>
+
+properties:
+  compatible:
+    const: thead,th1520-mbox
+
+  clocks:
+    items:
+      - description: Clock for the local mailbox
+      - description: Clock for remote ICU 0
+      - description: Clock for remote ICU 1
+      - description: Clock for remote ICU 2
+
+  clock-names:
+    items:
+      - const: clk-local
+      - const: clk-remote-icu0
+      - const: clk-remote-icu1
+      - const: clk-remote-icu2
+
+  reg:
+    items:
+      - description: Mailbox local base address
+      - description: Remote ICU 0 base address
+      - description: Remote ICU 1 base address
+      - description: Remote ICU 2 base address
+
+  reg-names:
+    items:
+      - const: local
+      - const: remote-icu0
+      - const: remote-icu1
+      - const: remote-icu2
+
+  interrupts:
+    maxItems: 1
+
+  '#mbox-cells':
+    const: 1
+    description:
+      The one and only cell describes destination CPU ID.
+
+required:
+  - compatible
+  - clocks
+  - clock-names
+  - reg
+  - reg-names
+  - interrupts
+  - '#mbox-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/thead,th1520-clk-ap.h>
+    soc {
+      #address-cells = <2>;
+      #size-cells = <2>;
+      mailbox@ffffc38000 {
+        compatible = "thead,th1520-mbox";
+        reg = <0xff 0xffc38000 0x0 0x4000>,
+              <0xff 0xffc44000 0x0 0x1000>,
+              <0xff 0xffc4c000 0x0 0x1000>,
+              <0xff 0xffc54000 0x0 0x1000>;
+        reg-names = "local", "remote-icu0", "remote-icu1", "remote-icu2";
+        clocks = <&clk CLK_MBOX0>, <&clk CLK_MBOX1>, <&clk CLK_MBOX2>,
+                 <&clk CLK_MBOX3>;
+        clock-names = "clk-local", "clk-remote-icu0", "clk-remote-icu1",
+                      "clk-remote-icu2";
+        interrupts = <28>;
+        #mbox-cells = <1>;
+      };
+    };

MAINTAINERS

@@ -19869,6 +19869,7 @@ L:	linux-riscv@lists.infradead.org
 S:	Maintained
 T:	git https://github.com/pdp7/linux.git
 F:	Documentation/devicetree/bindings/clock/thead,th1520-clk-ap.yaml
+F:	Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml
 F:	arch/riscv/boot/dts/thead/
 F:	drivers/clk/thead/clk-th1520-ap.c
 F:	drivers/mailbox/mailbox-th1520.c