.. SPDX-License-Identifier: GPL-2.0
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======
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Graphs
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======
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_DSD
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====
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_DSD (Device Specific Data) [7] is a predefined ACPI device
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configuration object that can be used to convey information on
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hardware features which are not specifically covered by the ACPI
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specification [1][6]. There are two _DSD extensions that are relevant
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for graphs: property [4] and hierarchical data extensions [5]. The
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property extension provides generic key-value pairs whereas the
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hierarchical data extension supports nodes with references to other
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nodes, forming a tree. The nodes in the tree may contain properties as
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defined by the property extension. The two extensions together provide
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a tree-like structure with zero or more properties (key-value pairs)
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in each node of the tree.
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The data structure may be accessed at runtime by using the device_*
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and fwnode_* functions defined in include/linux/fwnode.h .
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Fwnode represents a generic firmware node object. It is independent on
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the firmware type. In ACPI, fwnodes are _DSD hierarchical data
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extensions objects. A device's _DSD object is represented by an
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fwnode.
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The data structure may be referenced to elsewhere in the ACPI tables
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by using a hard reference to the device itself and an index to the
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hierarchical data extension array on each depth.
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Ports and endpoints
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===================
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The port and endpoint concepts are very similar to those in Devicetree
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[3]. A port represents an interface in a device, and an endpoint
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represents a connection to that interface.
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All port nodes are located under the device's "_DSD" node in the hierarchical
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data extension tree. The data extension related to each port node must begin
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with "port" and must be followed by the "@" character and the number of the
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port as its key. The target object it refers to should be called "PRTX", where
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"X" is the number of the port. An example of such a package would be::
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Package() { "port@4", "PRT4" }
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Further on, endpoints are located under the port nodes. The hierarchical
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data extension key of the endpoint nodes must begin with
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"endpoint" and must be followed by the "@" character and the number of the
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endpoint. The object it refers to should be called "EPXY", where "X" is the
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number of the port and "Y" is the number of the endpoint. An example of such a
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package would be::
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Package() { "endpoint@0", "EP40" }
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Each port node contains a property extension key "port", the value of which is
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the number of the port. Each endpoint is similarly numbered with a property
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extension key "reg", the value of which is the number of the endpoint. Port
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numbers must be unique within a device and endpoint numbers must be unique
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within a port. If a device object may only has a single port, then the number
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of that port shall be zero. Similarly, if a port may only have a single
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endpoint, the number of that endpoint shall be zero.
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The endpoint reference uses property extension with "remote-endpoint" property
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name followed by a reference in the same package. Such references consist of
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the remote device reference, the first package entry of the port data extension
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reference under the device and finally the first package entry of the endpoint
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data extension reference under the port. Individual references thus appear as::
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Package() { device, "port@X", "endpoint@Y" }
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In the above example, "X" is the number of the port and "Y" is the number of
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the endpoint.
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The references to endpoints must be always done both ways, to the
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remote endpoint and back from the referred remote endpoint node.
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A simple example of this is show below::
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Scope (\_SB.PCI0.I2C2)
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{
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Device (CAM0)
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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 () { "compatible", Package () { "nokia,smia" } },
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},
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ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
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Package () {
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Package () { "port@0", "PRT0" },
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}
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})
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Name (PRT0, 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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},
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ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
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Package () {
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Package () { "endpoint@0", "EP00" },
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}
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})
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Name (EP00, 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 () { "remote-endpoint", Package() { \_SB.PCI0.ISP, "port@4", "endpoint@0" } },
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}
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})
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}
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}
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Scope (\_SB.PCI0)
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{
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Device (ISP)
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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 () { "port@4", "PRT4" },
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}
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})
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Name (PRT4, Package() {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () { "reg", 4 }, /* CSI-2 port number */
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},
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ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
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Package () {
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Package () { "endpoint@0", "EP40" },
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}
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})
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Name (EP40, 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 () { "remote-endpoint", Package () { \_SB.PCI0.I2C2.CAM0, "port@0", "endpoint@0" } },
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}
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})
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}
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}
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Here, the port 0 of the "CAM0" device is connected to the port 4 of
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the "ISP" device and vice versa.
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References
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==========
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[1] _DSD (Device Specific Data) Implementation Guide.
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https://www.uefi.org/sites/default/files/resources/_DSD-implementation-guide-toplevel-1_1.htm,
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referenced 2016-10-03.
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[2] Devicetree. https://www.devicetree.org, referenced 2016-10-03.
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[3] Documentation/devicetree/bindings/graph.txt
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[4] Device Properties UUID For _DSD.
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https://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf,
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referenced 2016-10-04.
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[5] Hierarchical Data Extension UUID For _DSD.
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https://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.1.pdf,
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referenced 2016-10-04.
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[6] Advanced Configuration and Power Interface Specification.
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https://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf,
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referenced 2016-10-04.
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[7] _DSD Device Properties Usage Rules.
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:doc:`../DSD-properties-rules`
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