xref: /linux/Documentation/firmware-guide/acpi/dsd/data-node-references.rst (revision 03ab8e6297acd1bc0eedaa050e2a1635c576fd11) 
1.. SPDX-License-Identifier: GPL-2.0
2.. include:: <isonum.txt>
3
4===================================
5Referencing hierarchical data nodes
6===================================
7
8:Copyright: |copy| 2018, 2021 Intel Corporation
9:Author: Sakari Ailus <sakari.ailus@linux.intel.com>
10
11ACPI in general allows referring to device objects in the tree only.
12Hierarchical data extension nodes may not be referred to directly, hence this
13document defines a scheme to implement such references.
14
15A reference consist of the device object name followed by one or more
16hierarchical data extension [dsd-guide] keys. Specifically, the hierarchical
17data extension node which is referred to by the key shall lie directly under
18the parent object i.e. either the device object or another hierarchical data
19extension node.
20
21The keys in the hierarchical data nodes shall consist of the name of the node,
22"@" character and the number of the node in hexadecimal notation (without pre-
23or postfixes). The same ACPI object shall include the _DSD property extension
24with a property "reg" that shall have the same numerical value as the number of
25the node.
26
27In case a hierarchical data extensions node has no numerical value, then the
28"reg" property shall be omitted from the ACPI object's _DSD properties and the
29"@" character and the number shall be omitted from the hierarchical data
30extension key.
31
32
33Example
34=======
35
36In the ASL snippet below, the "reference" _DSD property contains a
37device object reference to DEV0 and under that device object, a
38hierarchical data extension key "node@1" referring to the NOD1 object
39and lastly, a hierarchical data extension key "anothernode" referring to
40the ANOD object which is also the final target node of the reference.
41::
42
43	Device (DEV0)
44	{
45	    Name (_DSD, Package () {
46		ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
47		Package () {
48		    Package () { "node@0", "NOD0" },
49		    Package () { "node@1", "NOD1" },
50		}
51	    })
52	    Name (NOD0, Package() {
53		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
54		Package () {
55		    Package () { "reg", 0 },
56		    Package () { "random-property", 3 },
57		}
58	    })
59	    Name (NOD1, Package() {
60		ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
61		Package () {
62		    Package () { "reg", 1 },
63		    Package () { "anothernode", "ANOD" },
64		}
65	    })
66	    Name (ANOD, Package() {
67		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
68		Package () {
69		    Package () { "random-property", 0 },
70		}
71	    })
72	}
73
74	Device (DEV1)
75	{
76	    Name (_DSD, Package () {
77		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
78		Package () {
79		    Package () {
80			"reference", Package () {
81			    ^DEV0, "node@1", "anothernode"
82			}
83		    },
84		}
85	    })
86	}
87
88Please also see a graph example in
89Documentation/firmware-guide/acpi/dsd/graph.rst.
90
91References
92==========
93
94[dsd-guide] DSD Guide.
95    https://github.com/UEFI/DSD-Guide/blob/main/dsd-guide.adoc, referenced
96    2021-11-30.
97