ARCv2: SMP: intc: IDU 2nd level intc for dynamic IRQ distribution

Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Documentation/devicetree/bindings/arc/archs-idu-intc.txt

@@ -0,0 +1,46 @@
+* ARC-HS Interrupt Distribution Unit
+
+  This optional 2nd level interrupt controller can be used in SMP configurations for
+  dynamic IRQ routing, load balancing of common/external IRQs towards core intc.
+
+Properties:
+
+- compatible: "snps,archs-idu-intc"
+- interrupt-controller: This is an interrupt controller.
+- interrupt-parent: <reference to parent core intc>
+- #interrupt-cells: Must be <2>.
+- interrupts: <...> specifies the upstream core irqs
+
+  First cell specifies the "common" IRQ from peripheral to IDU
+  Second cell specifies the irq distribution mode to cores
+     0=Round Robin; 1=cpu0, 2=cpu1, 4=cpu2, 8=cpu3
+
+  intc accessed via the special ARC AUX register interface, hence "reg" property
+  is not specified.
+
+Example:
+	core_intc: core-interrupt-controller {
+		compatible = "snps,archs-intc";
+		interrupt-controller;
+		#interrupt-cells = <1>;
+	};
+
+	idu_intc: idu-interrupt-controller {
+		compatible = "snps,archs-idu-intc";
+		interrupt-controller;
+		interrupt-parent = <&core_intc>;
+
+		/*
+		 * <hwirq  distribution>
+		 * distribution: 0=RR; 1=cpu0, 2=cpu1, 4=cpu2, 8=cpu3
+		 */
+		#interrupt-cells = <2>;
+
+		/* upstream core irqs: downstream these are "COMMON" irq 0,1..  */
+		interrupts = <24 25 26 27 28 29 30 31>;
+	};
+
+	some_device: serial@c0fc1000 {
+		interrupt-parent = <&idu_intc>;
+		interrupts = <0 0>;	/* upstream idu IRQ #24, Round Robin */
+	};