BACKPORT: perf: Add Arm CMN-600 DT binding

Document the requirements for the CMN-600 DT binding. The internal
topology is almost entirely discoverable by walking a tree of ID
registers, but sadly both the starting point for that walk and the
exact format of those registers are configuration-dependent and not
discoverable from some sane fixed location. Oh well.

This patch is part of the eMAG2 CMN-600 PMU patch set.
This patch is backported from:
http://www.linux-arm.org/git?p=linux-rm.git;a=commit;h=d92b2ecc303fba919a57d699ae4fd297ced2e91c

Signed-off-by: Robin Murphy <[email protected]>
Signed-off-by: Khuong Dinh <[email protected]>

Documentation/devicetree/bindings/perf/arm-cmn.txt

@@ -0,0 +1,23 @@
+* ARM CMN (Coherent Mesh Network) Performance Monitor
+
+** Required properties:
+
+- compatible	: Should be "arm,cmn-600"
+
+- reg		: Physical address of the base (PERIPHBASE) and size
+		  (up to 64MB) of the configuration address space.
+
+- interrupts	: PMU overflow interrupts, one per implemented DTC.
+
+- arm,root-node	: Offset from PERIPHBASE of the configuration discovery
+		  node (see TRM definition of ROOTNODEBASE).
+
+Example:
+
+	cmn@50000000 {
+		compatible = "arm,cmn-600";
+		reg = <0x0 0x50000000 0x0 0x4000000>;
+		/* 4x2 mesh with one DTC, and CFG node at 0,1,1,0 */
+		interrupts = <GIC_SPI 46 IRQ_TYPE_LEVEL_HIGH>;
+		arm,root-node = <0x104000>;
+	};