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Commit b10134a3 authored by Sakari Ailus's avatar Sakari Ailus Committed by Rafael J. Wysocki
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ACPI: property: Document hierarchical data extension references 



Add documentation on how to refer to hierarchical data nodes in a
generic way. This brings ACPI to feature parity with Device Tree in
terms of being able to refer to any node in the tree.

Signed-off-by: default avatarSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 4eb0c3bf

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

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Original line number Diff line number Diff line 
Copyright (C) 2018 Intel Corporation

Author: Sakari Ailus <sakari.ailus@linux.intel.com>





Referencing hierarchical data nodes

-----------------------------------



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 [1] 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.



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.



	Device (DEV0)

	{

	    Name (_DSD, Package () {

		ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),

		Package () {

		    Package () { "node", NODE },

		}

	    })

	    Name (NODE, Package() {

		ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),

		Package () {

		    Package () { "anothernode", ANOD },

		}

	    })

	    Name (ANOD, Package() {

		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),

		Package () {

		    Package () { "random-property", 0 },

		}

	    })

	}



	Device (DEV1)

	{

	    Name (_DSD, Package () {

		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),

		Package () {

		    Package () { "reference", ^DEV0, "node", "anothernode" },

		}

	    })

	}





References

----------



[1] Hierarchical Data Extension UUID For _DSD.

    <URL:http://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.1.pdf>,

    referenced 2018-07-17.



[2] Device Properties UUID For _DSD.

    <URL:http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf>,

    referenced 2016-10-04.