Documentation: ACPI: Use all-string data node references

Document that references to data nodes shall use string-only references
instead of a device reference and a succession of the first package
entries of hierarchical data node references.

Fixes: 9880702d123f ("ACPI: property: Support using strings in reference properties")
Cc: 6.8+ <stable@vger.kernel.org> # 6.8+
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://patch.msgid.link/20250409084738.3657079-1-sakari.ailus@linux.intel.com
[ rjw: Clarifying edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 12 insertions, 14 deletions

diff --git a/Documentation/firmware-guide/acpi/dsd/data-node-references.rst b/Documentation/firmware-guide/acpi/dsd/data-node-references.rst
index 8d8b53e96bcf..ccb4b153e6f2 100644
--- a/Documentation/firmware-guide/acpi/dsd/data-node-references.rst
+++ b/Documentation/firmware-guide/acpi/dsd/data-node-references.rst
@@ -12,11 +12,14 @@ ACPI in general allows referring to device objects in the tree only.
 Hierarchical data extension nodes may not be referred to directly, hence this
 document defines a scheme to implement such references.
 
-A reference consist of the device object name followed by one or more
-hierarchical data extension [dsd-guide] keys. Specifically, the hierarchical
-data 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.
+A reference to a _DSD hierarchical data node is a string consisting of a
+device object reference followed by a dot (".") and a relative path to a data
+node object. Do not use non-string references as this will produce a copy of
+the hierarchical data node, not a reference!
+
+The hierarchical data extension node which is referred to shall be located
+directly under its parent object i.e. either the device object or another
+hierarchical data extension node [dsd-guide].
 
 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-
@@ -33,11 +36,9 @@ extension key.
 Example
 =======
 
-In the ASL snippet below, the "reference" _DSD property contains a
-device object reference to DEV0 and under that device object, a
-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.
+In the ASL snippet below, the "reference" _DSD property contains a string
+reference to a hierarchical data extension node ANOD under DEV0 under the parent
+of DEV1. ANOD is also the final target node of the reference.
 ::
 
 	Device (DEV0)
@@ -76,10 +77,7 @@ the ANOD object which is also the final target node of the reference.
 	    Name (_DSD, Package () {
 		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
 		Package () {
-		    Package () {
-			"reference", Package () {
-			    ^DEV0, "node@1", "anothernode"
-			}
+		    Package () { "reference", "^DEV0.ANOD" }
 		    },
 		}
 	    })