dt-bindings: interrupt-controller: Add EcoNet EN751221 INTC

Document the device tree binding for the interrupt controller in the
EcoNet EN751221 MIPS SoC.

Signed-off-by: Caleb James DeLisle <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]

Documentation/devicetree/bindings/interrupt-controller/econet,en751221-intc.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/interrupt-controller/econet,en751221-intc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: EcoNet EN751221 Interrupt Controller
+
+maintainers:
+  - Caleb James DeLisle <[e-mail]>
+
+description:
+  The EcoNet EN751221 Interrupt Controller is a simple interrupt controller
+  designed for the MIPS 34Kc MT SMP processor with 2 VPEs. Each interrupt can
+  be routed to either VPE but not both, so to support per-CPU interrupts, a
+  secondary IRQ number is allocated to control masking/unmasking on VPE#1. For
+  lack of a better term we call these "shadow interrupts". The assignment of
+  shadow interrupts is defined by the SoC integrator when wiring the interrupt
+  lines, so they are configurable in the device tree.
+
+allOf:
+  - $ref: /schemas/interrupt-controller.yaml#
+
+properties:
+  compatible:
+    const: econet,en751221-intc
+
+  reg:
+    maxItems: 1
+
+  "#interrupt-cells":
+    const: 1
+
+  interrupt-controller: true
+
+  interrupts:
+    maxItems: 1
+    description: Interrupt line connecting this controller to its parent.
+
+  econet,shadow-interrupts:
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    description:
+      An array of interrupt number pairs where each pair represents a shadow
+      interrupt relationship. The first number in each pair is the primary IRQ,
+      and the second is its shadow IRQ used for VPE#1 control. For example,
+      <8 3> means IRQ 8 is shadowed by IRQ 3, so IRQ 3 cannot be mapped, but
+      when VPE#1 requests IRQ 8, it will manipulate the IRQ 3 mask bit.
+    minItems: 1
+    maxItems: 20
+    items:
+      items:
+        - description: primary per-CPU IRQ
+        - description: shadow IRQ number
+
+required:
+  - compatible
+  - reg
+  - interrupt-controller
+  - "#interrupt-cells"
+  - interrupts
+
+additionalProperties: false
+
+examples:
+  - |
+    interrupt-controller@1fb40000 {
+        compatible = "econet,en751221-intc";
+        reg = <0x1fb40000 0x100>;
+
+        interrupt-controller;
+        #interrupt-cells = <1>;
+
+        interrupt-parent = <&cpuintc>;
+        interrupts = <2>;
+
+        econet,shadow-interrupts = <7 2>, <8 3>, <13 12>, <30 29>;
+    };
+...