dt-bindings: mailbox: add cix,sky1-mbox

Add a dt-binding for the Cixtech Mailbox Controller.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Peter Chen <peter.chen@cixtech.com>
Signed-off-by: Guomin Chen <Guomin.Chen@cixtech.com>
Signed-off-by: Lihua Liu <Lihua.Liu@cixtech.com>
Signed-off-by: Peter Chen <peter.chen@cixtech.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Documentation/devicetree/bindings/mailbox/cix,sky1-mbox.yaml

@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/cix,sky1-mbox.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Cixtech mailbox controller
+
+maintainers:
+  - Guomin Chen <Guomin.Chen@cixtech.com>
+
+description:
+  The Cixtech mailbox controller, used in the Cixtech Sky1 SoC,
+  is used for message transmission between multiple processors
+  within the SoC, such as the AP, PM, audio DSP, SensorHub MCU,
+  and others
+
+  Each Cixtech mailbox controller is unidirectional, so they are
+  typically used in pairs-one for receiving and one for transmitting.
+
+  Each Cixtech mailbox supports 11 channels with different transmission modes
+    channel 0-7 - Fast channel with 32bit transmit register and IRQ support
+    channel 8   - Doorbell mode,using the mailbox as an interrupt-generating
+                   mechanism.
+    channel 9   - Fifo based channel with 32*32bit depth fifo and IRQ support
+    channel 10  - Reg based channel with 32*32bit transmit register and
+                   Doorbell+transmit acknowledgment IRQ support
+
+  In the CIX Sky1 SoC use case, there are 4 pairs of mailbox controllers
+    AP <--> PM - using Doorbell transfer mode
+    AP <--> SE - using REG transfer mode
+    AP <--> DSP - using FIFO transfer mode
+    AP <--> SensorHub - using FIFO transfer mode
+
+properties:
+  compatible:
+    const: cix,sky1-mbox
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  "#mbox-cells":
+    const: 1
+
+  cix,mbox-dir:
+    $ref: /schemas/types.yaml#/definitions/string
+    description: Direction of the mailbox relative to the AP
+    enum: [tx, rx]
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - "#mbox-cells"
+  - cix,mbox-dir
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    soc {
+        #address-cells = <2>;
+        #size-cells = <2>;
+
+        mbox_ap2pm: mailbox@30000000 {
+            compatible = "cix,sky1-mbox";
+            reg = <0 0x30000000 0 0x10000>;
+            interrupts = <GIC_SPI 136 IRQ_TYPE_LEVEL_HIGH 0>;
+            #mbox-cells = <1>;
+            cix,mbox-dir = "tx";
+        };
+    };