97 lines · plain
1.. SPDX-License-Identifier: GPL-2.02.. include:: <isonum.txt>3 4===================================5Referencing hierarchical data nodes6===================================7 8:Copyright: |copy| 2018, 2021 Intel Corporation9: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 this13document defines a scheme to implement such references.14 15A reference consist of the device object name followed by one or more16hierarchical data extension [dsd-guide] keys. Specifically, the hierarchical17data extension node which is referred to by the key shall lie directly under18the parent object i.e. either the device object or another hierarchical data19extension 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 extension24with a property "reg" that shall have the same numerical value as the number of25the node.26 27In case a hierarchical data extensions node has no numerical value, then the28"reg" property shall be omitted from the ACPI object's _DSD properties and the29"@" character and the number shall be omitted from the hierarchical data30extension key.31 32 33Example34=======35 36In the ASL snippet below, the "reference" _DSD property contains a37device object reference to DEV0 and under that device object, a38hierarchical data extension key "node@1" referring to the NOD1 object39and lastly, a hierarchical data extension key "anothernode" referring to40the 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 in89Documentation/firmware-guide/acpi/dsd/graph.rst.90 91References92==========93 94[dsd-guide] DSD Guide.95 https://github.com/UEFI/DSD-Guide/blob/main/dsd-guide.adoc, referenced96 2021-11-30.97