94 lines
2.8 KiB
ReStructuredText
94 lines
2.8 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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.. include:: <isonum.txt>
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===================================
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Referencing hierarchical data nodes
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===================================
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:Copyright: |copy| 2018, 2021 Intel Corporation
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:Author: Sakari Ailus <sakari.ailus@linux.intel.com>
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ACPI in general allows referring to device objects in the tree only.
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Hierarchical data extension nodes may not be referred to directly, hence this
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document defines a scheme to implement such references.
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A reference to a _DSD hierarchical data node is a string consisting of a
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device object reference followed by a dot (".") and a relative path to a data
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node object. Do not use non-string references as this will produce a copy of
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the hierarchical data node, not a reference!
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The hierarchical data extension node which is referred to shall be located
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directly under its parent object i.e. either the device object or another
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hierarchical data extension node [dsd-guide].
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The keys in the hierarchical data nodes shall consist of the name of the node,
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"@" character and the number of the node in hexadecimal notation (without pre-
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or postfixes). The same ACPI object shall include the _DSD property extension
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with a property "reg" that shall have the same numerical value as the number of
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the node.
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In case a hierarchical data extensions node has no numerical value, then the
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"reg" property shall be omitted from the ACPI object's _DSD properties and the
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"@" character and the number shall be omitted from the hierarchical data
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extension key.
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Example
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=======
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In the ASL snippet below, the "reference" _DSD property contains a string
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reference to a hierarchical data extension node ANOD under DEV0 under the parent
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of DEV1. ANOD is also the final target node of the reference.
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::
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Device (DEV0)
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{
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Name (_DSD, Package () {
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ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
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Package () {
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Package () { "node@0", "NOD0" },
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Package () { "node@1", "NOD1" },
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}
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})
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Name (NOD0, Package() {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () { "reg", 0 },
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Package () { "random-property", 3 },
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}
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})
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Name (NOD1, Package() {
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ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
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Package () {
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Package () { "reg", 1 },
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Package () { "anothernode", "ANOD" },
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}
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})
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Name (ANOD, Package() {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () { "random-property", 0 },
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}
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})
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}
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Device (DEV1)
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{
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Name (_DSD, Package () {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () { "reference", "^DEV0.ANOD" }
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},
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}
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})
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}
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Please also see a graph example in
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Documentation/firmware-guide/acpi/dsd/graph.rst.
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References
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==========
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[dsd-guide] DSD Guide.
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https://github.com/UEFI/DSD-Guide/blob/main/dsd-guide.adoc, referenced
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2021-11-30.
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