dt-bindings: interrupt-controller: Add Loongson PCH MSI

Add binding for Loongson PCH MSI controller.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200528152757.1028711-7-jiaxun.yang@flygoat.com

Documentation/devicetree/bindings/interrupt-controller/loongson,pch-msi.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/interrupt-controller/loongson,pch-msi.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Loongson PCH MSI Controller
+
+maintainers:
+  - Jiaxun Yang <jiaxun.yang@flygoat.com>
+
+description:
+  This interrupt controller is found in the Loongson LS7A family of PCH for
+  transforming interrupts from PCIe MSI into HyperTransport vectorized
+  interrupts.
+
+properties:
+  compatible:
+    const: loongson,pch-msi-1.0
+
+  reg:
+    maxItems: 1
+
+  loongson,msi-base-vec:
+    description:
+      u32 value of the base of parent HyperTransport vector allocated
+      to PCH MSI.
+    allOf:
+      - $ref: "/schemas/types.yaml#/definitions/uint32"
+      - minimum: 0
+        maximum: 255
+
+  loongson,msi-num-vecs:
+    description:
+      u32 value of the number of parent HyperTransport vectors allocated
+      to PCH MSI.
+    allOf:
+      - $ref: "/schemas/types.yaml#/definitions/uint32"
+      - minimum: 1
+        maximum: 256
+
+  msi-controller: true
+
+required:
+  - compatible
+  - reg
+  - msi-controller
+  - loongson,msi-base-vec
+  - loongson,msi-num-vecs
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    msi: msi-controller@2ff00000 {
+      compatible = "loongson,pch-msi-1.0";
+      reg = <0x2ff00000 0x4>;
+      msi-controller;
+      loongson,msi-base-vec = <64>;
+      loongson,msi-num-vecs = <64>;
+      interrupt-parent = <&htvec>;
+    };
+...