1 This file has moved to graph.yaml in dt-schema !! 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
>> 22 Documentation/devicetree/bindings/media/video-interfaces.txt.
>> 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 to 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, it
>> 93 must not point to anything other than the local endpoint. Two endpoints with
>> 94 their '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 Required properties
>> 114 -------------------
>> 115
>> 116 If there is more than one 'port' or more than one 'endpoint' node or 'reg'
>> 117 property present in the port and/or endpoint nodes then the following
>> 118 properties are required in a relevant parent node:
>> 119
>> 120 - #address-cells : number of cells required to define port/endpoint
>> 121 identifier, should be 1.
>> 122 - #size-cells : should be zero.
>> 123
>> 124 Optional endpoint properties
>> 125 ----------------------------
>> 126
>> 127 - remote-endpoint: phandle to an 'endpoint' subnode of a remote device node.
>> 128
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