dt-bindings: interconnect: Document the support of optional path tag

Let's document that we now support specifying path tag information in the
arg cells of the 'interconnects' DT property. This information would be
populated when the xlate_extended() callback is used.

Specifying the tag in DT will allow the interconnect framework to do the
aggregation based on the tag automatically. The users can still use the
icc_set_tag() API if/when needed.

Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200903133134.17201-3-georgi.djakov@linaro.org
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>

Author: Georgi Djakov

Documentation/devicetree/bindings/interconnect/interconnect.txt

@@ -19,7 +19,8 @@ directly.
 Required properties:
 - compatible : contains the interconnect provider compatible string
 - #interconnect-cells : number of cells in a interconnect specifier needed to
-			encode the interconnect node id
+			encode the interconnect node id and optionally add a
+			path tag
 
 Example:
 
@@ -44,6 +45,10 @@ components it has to interact with.
 Required properties:
 interconnects : Pairs of phandles and interconnect provider specifier to denote
 	        the edge source and destination ports of the interconnect path.
+		An optional path tag value could specified as additional argument
+		to both endpoints and in such cases, this information will be passed
+		to the interconnect framework to do aggregation based on the attached
+		tag.
 
 Optional properties:
 interconnect-names : List of interconnect path name strings sorted in the same
@@ -62,3 +67,20 @@ Example:
 		interconnects = <&pnoc MASTER_SDCC_1 &bimc SLAVE_EBI_CH0>;
 		interconnect-names = "sdhc-mem";
 	};
+
+Example with path tags:
+
+	gnoc: interconnect@17900000 {
+		...
+		interconnect-cells = <2>;
+	};
+
+	mnoc: interconnect@1380000 {
+		...
+		interconnect-cells = <2>;
+	};
+
+	cpu@0 {
+		...
+		interconnects = <&gnoc MASTER_APPSS_PROC 3 &mnoc SLAVE_EBI1 3>;
+	}