1 .. SPDX-License-Identifier: GPL-2.0
2
3 ======
4 Graphs
5 ======
6
7 _DSD
8 ====
9
10 _DSD (Device Specific Data) [dsd-guide] is a predefined ACPI device
11 configuration object that can be used to convey information on
12 hardware features which are not specifically covered by the ACPI
13 specification [acpi]. There are two _DSD extensions that are relevant
14 for graphs: property [dsd-guide] and hierarchical data extensions. The
15 property extension provides generic key-value pairs whereas the
16 hierarchical data extension supports nodes with references to other
17 nodes, forming a tree. The nodes in the tree may contain properties as
18 defined by the property extension. The two extensions together provide
19 a tree-like structure with zero or more properties (key-value pairs)
20 in each node of the tree.
21
22 The data structure may be accessed at runtime by using the device_*
23 and fwnode_* functions defined in include/linux/fwnode.h .
24
25 Fwnode represents a generic firmware node object. It is independent on
26 the firmware type. In ACPI, fwnodes are _DSD hierarchical data
27 extensions objects. A device's _DSD object is represented by an
28 fwnode.
29
30 The data structure may be referenced to elsewhere in the ACPI tables
31 by using a hard reference to the device itself and an index to the
32 hierarchical data extension array on each depth.
33
34
35 Ports and endpoints
36 ===================
37
38 The port and endpoint concepts are very similar to those in Devicetree
39 [devicetree, graph-bindings]. A port represents an interface in a device, and
40 an endpoint represents a connection to that interface. Also see [data-node-ref]
41 for generic data node references.
42
43 All port nodes are located under the device's "_DSD" node in the hierarchical
44 data extension tree. The data extension related to each port node must begin
45 with "port" and must be followed by the "@" character and the number of the
46 port as its key. The target object it refers to should be called "PRTX", where
47 "X" is the number of the port. An example of such a package would be::
48
49 Package() { "port@4", "PRT4" }
50
51 Further on, endpoints are located under the port nodes. The hierarchical
52 data extension key of the endpoint nodes must begin with
53 "endpoint" and must be followed by the "@" character and the number of the
54 endpoint. The object it refers to should be called "EPXY", where "X" is the
55 number of the port and "Y" is the number of the endpoint. An example of such a
56 package would be::
57
58 Package() { "endpoint@0", "EP40" }
59
60 Each port node contains a property extension key "port", the value of which is
61 the number of the port. Each endpoint is similarly numbered with a property
62 extension key "reg", the value of which is the number of the endpoint. Port
63 numbers must be unique within a device and endpoint numbers must be unique
64 within a port. If a device object may only has a single port, then the number
65 of that port shall be zero. Similarly, if a port may only have a single
66 endpoint, the number of that endpoint shall be zero.
67
68 The endpoint reference uses property extension with "remote-endpoint" property
69 name followed by a reference in the same package. Such references consist of
70 the remote device reference, the first package entry of the port data extension
71 reference under the device and finally the first package entry of the endpoint
72 data extension reference under the port. Individual references thus appear as::
73
74 Package() { device, "port@X", "endpoint@Y" }
75
76 In the above example, "X" is the number of the port and "Y" is the number of
77 the endpoint.
78
79 The references to endpoints must be always done both ways, to the
80 remote endpoint and back from the referred remote endpoint node.
81
82 A simple example of this is show below::
83
84 Scope (\_SB.PCI0.I2C2)
85 {
86 Device (CAM0)
87 {
88 Name (_DSD, Package () {
89 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
90 Package () {
91 Package () { "compatible", Package () { "nokia,smia" } },
92 },
93 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
94 Package () {
95 Package () { "port@0", "PRT0" },
96 }
97 })
98 Name (PRT0, Package() {
99 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
100 Package () {
101 Package () { "reg", 0 },
102 },
103 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
104 Package () {
105 Package () { "endpoint@0", "EP00" },
106 }
107 })
108 Name (EP00, Package() {
109 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
110 Package () {
111 Package () { "reg", 0 },
112 Package () { "remote-endpoint", Package() { \_SB.PCI0.ISP, "port@4", "endpoint@0" } },
113 }
114 })
115 }
116 }
117
118 Scope (\_SB.PCI0)
119 {
120 Device (ISP)
121 {
122 Name (_DSD, Package () {
123 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
124 Package () {
125 Package () { "port@4", "PRT4" },
126 }
127 })
128
129 Name (PRT4, Package() {
130 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
131 Package () {
132 Package () { "reg", 4 }, /* CSI-2 port number */
133 },
134 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
135 Package () {
136 Package () { "endpoint@0", "EP40" },
137 }
138 })
139
140 Name (EP40, Package() {
141 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
142 Package () {
143 Package () { "reg", 0 },
144 Package () { "remote-endpoint", Package () { \_SB.PCI0.I2C2.CAM0, "port@0", "endpoint@0" } },
145 }
146 })
147 }
148 }
149
150 Here, the port 0 of the "CAM0" device is connected to the port 4 of
151 the "ISP" device and vice versa.
152
153
154 References
155 ==========
156
157 [acpi] Advanced Configuration and Power Interface Specification.
158 https://uefi.org/specifications/ACPI/6.4/, referenced 2021-11-30.
159
160 [data-node-ref] Documentation/firmware-guide/acpi/dsd/data-node-references.rst
161
162 [devicetree] Devicetree. https://www.devicetree.org, referenced 2016-10-03.
163
164 [dsd-guide] DSD Guide.
165 https://github.com/UEFI/DSD-Guide/blob/main/dsd-guide.adoc, referenced
166 2021-11-30.
167
168 [dsd-rules] _DSD Device Properties Usage Rules.
169 Documentation/firmware-guide/acpi/DSD-properties-rules.rst
170
171 [graph-bindings] Common bindings for device graphs (Devicetree).
172 https://github.com/devicetree-org/dt-schema/blob/main/schemas/graph.yaml,
173 referenced 2021-11-30.
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