ACPI: property: Document key numbering for hierarchical data extensio…

…n refs

As part of the hierarchical data extension key naming, introduce numbering
scheme for the nodes that may be referred to using hierarchical data
extension references. This allows iterating over particular kind of nodes
recognised by the node name whilst allowing numbering the nodes, bringing
ACPI to feature parity with DT in this respect.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/acpi/dsd/data-node-references.txt

@@ -15,24 +15,43 @@ extension node which is referred to by the key shall lie directly under the
 parent object i.e. either the device object or another hierarchical data
 extension node.
 
+The keys in the hierarchical data nodes shall consist of the name of the node,
+"@" character and the number of the node in hexadecimal notation (without pre-
+or postfixes). The same ACPI object shall include the _DSD property extension
+with a property "reg" that shall have the same numerical value as the number of
+the node.
+
+In case a hierarchical data extensions node has no numerical value, then the
+"reg" property shall be omitted from the ACPI object's _DSD properties and the
+"@" character and the number shall be omitted from the hierarchical data
+extension key.
+
+
 Example
 -------
 
 	In the ASL snippet below, the "reference" _DSD property [2] contains a
 	device object reference to DEV0 and under that device object, a
-	hierarchical data extension key "node" referring to the NODE object and
-	lastly, a hierarchical data extension key "anothernode" referring to the
-	ANOD object which is also the final target of the reference.
+	hierarchical data extension key "node@1" referring to the NOD1 object
+	and lastly, a hierarchical data extension key "anothernode" referring to
+	the ANOD object which is also the final target node of the reference.
 
 	Device (DEV0)
 	{
 	    Name (_DSD, Package () {
 		ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
 		Package () {
-		    Package () { "node", NODE },
+		    Package () { "node@0", NOD0 },
+		    Package () { "node@1", NOD1 },
+		}
+	    })
+	    Name (NOD0, Package() {
+		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+		Package () {
+		    Package () { "random-property", 3 },
 		}
 	    })
-	    Name (NODE, Package() {
+	    Name (NOD1, Package() {
 		ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
 		Package () {
 		    Package () { "anothernode", ANOD },
@@ -51,7 +70,7 @@ Example
 	    Name (_DSD, Package () {
 		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
 		Package () {
-		    Package () { "reference", ^DEV0, "node", "anothernode" },
+		    Package () { "reference", ^DEV0, "node@1", "anothernode" },
 		}
 	    })
 	}