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1 | Common bindings for device graphs |
2 | ||
3 | General concept | |
4 | --------------- | |
5 | ||
6 | The hierarchical organisation of the device tree is well suited to describe | |
7 | control flow to devices, but there can be more complex connections between | |
8 | devices that work together to form a logical compound device, following an | |
9 | arbitrarily complex graph. | |
10 | There already is a simple directed graph between devices tree nodes using | |
11 | phandle properties pointing to other nodes to describe connections that | |
12 | can not be inferred from device tree parent-child relationships. The device | |
13 | tree graph bindings described herein abstract more complex devices that can | |
14 | have multiple specifiable ports, each of which can be linked to one or more | |
15 | ports of other devices. | |
16 | ||
17 | These common bindings do not contain any information about the direction or | |
18 | type of the connections, they just map their existence. Specific properties | |
19 | may be described by specialized bindings depending on the type of connection. | |
20 | ||
21 | To see how this binding applies to video pipelines, for example, see | |
9d45e881 | 22 | Documentation/devicetree/bindings/media/video-interfaces.txt. |
4d56ed5a PZ |
23 | Here the ports describe data interfaces, and the links between them are |
24 | the connecting data buses. A single port with multiple connections can | |
25 | correspond to multiple devices being connected to the same physical bus. | |
26 | ||
27 | Organisation of ports and endpoints | |
28 | ----------------------------------- | |
29 | ||
30 | Ports are described by child 'port' nodes contained in the device node. | |
31 | Each port node contains an 'endpoint' subnode for each remote device port | |
32 | connected to this port. If a single port is connected to more than one | |
33 | remote device, an 'endpoint' child node must be provided for each link. | |
34 | If more than one port is present in a device node or there is more than one | |
35 | endpoint at a port, or a port node needs to be associated with a selected | |
36 | hardware interface, a common scheme using '#address-cells', '#size-cells' | |
37 | and 'reg' properties is used number the nodes. | |
38 | ||
39 | device { | |
40 | ... | |
41 | #address-cells = <1>; | |
42 | #size-cells = <0>; | |
43 | ||
44 | port@0 { | |
45 | #address-cells = <1>; | |
46 | #size-cells = <0>; | |
47 | reg = <0>; | |
48 | ||
49 | endpoint@0 { | |
50 | reg = <0>; | |
51 | ... | |
52 | }; | |
53 | endpoint@1 { | |
54 | reg = <1>; | |
55 | ... | |
56 | }; | |
57 | }; | |
58 | ||
59 | port@1 { | |
60 | reg = <1>; | |
61 | ||
62 | endpoint { ... }; | |
63 | }; | |
64 | }; | |
65 | ||
66 | All 'port' nodes can be grouped under an optional 'ports' node, which | |
67 | allows to specify #address-cells, #size-cells properties for the 'port' | |
68 | nodes independently from any other child device nodes a device might | |
69 | have. | |
70 | ||
71 | device { | |
72 | ... | |
73 | ports { | |
74 | #address-cells = <1>; | |
75 | #size-cells = <0>; | |
76 | ||
77 | port@0 { | |
78 | ... | |
79 | endpoint@0 { ... }; | |
80 | endpoint@1 { ... }; | |
81 | }; | |
82 | ||
83 | port@1 { ... }; | |
84 | }; | |
85 | }; | |
86 | ||
87 | Links between endpoints | |
88 | ----------------------- | |
89 | ||
90 | Each endpoint should contain a 'remote-endpoint' phandle property that points | |
91 | to the corresponding endpoint in the port of the remote device. In turn, the | |
92 | remote endpoint should contain a 'remote-endpoint' property. If it has one, | |
93 | it must not point to another than the local endpoint. Two endpoints with their | |
94 | 'remote-endpoint' phandles pointing at each other form a link between the | |
95 | containing ports. | |
96 | ||
97 | device-1 { | |
98 | port { | |
99 | device_1_output: endpoint { | |
100 | remote-endpoint = <&device_2_input>; | |
101 | }; | |
102 | }; | |
103 | }; | |
104 | ||
105 | device-2 { | |
106 | port { | |
107 | device_2_input: endpoint { | |
108 | remote-endpoint = <&device_1_output>; | |
109 | }; | |
110 | }; | |
111 | }; | |
112 | ||
113 | ||
114 | Required properties | |
115 | ------------------- | |
116 | ||
117 | If there is more than one 'port' or more than one 'endpoint' node or 'reg' | |
118 | property is present in port and/or endpoint nodes the following properties | |
119 | are required in a relevant parent node: | |
120 | ||
121 | - #address-cells : number of cells required to define port/endpoint | |
122 | identifier, should be 1. | |
123 | - #size-cells : should be zero. | |
124 | ||
125 | Optional endpoint properties | |
126 | ---------------------------- | |
127 | ||
128 | - remote-endpoint: phandle to an 'endpoint' subnode of a remote device node. | |
129 |