1 MIPI DSI (Display Serial Interface) busses
2 ==========================================
3
4 The MIPI Display Serial Interface specifies a serial bus and a protocol for
5 communication between a host and up to four peripherals. This document will
6 define the syntax used to represent a DSI bus in a device tree.
7
8 This document describes DSI bus-specific properties only or defines existing
9 standard properties in the context of the DSI bus.
10
11 Each DSI host provides a DSI bus. The DSI host controller's node contains a
12 set of properties that characterize the bus. Child nodes describe individual
13 peripherals on that bus.
14
15 The following assumes that only a single peripheral is connected to a DSI
16 host. Experience shows that this is true for the large majority of setups.
17
18 DSI host
19 ========
20
21 In addition to the standard properties and those defined by the parent bus of
22 a DSI host, the following properties apply to a node representing a DSI host.
23
24 Required properties:
25 - #address-cells: The number of cells required to represent an address on the
26 bus. DSI peripherals are addressed using a 2-bit virtual channel number, so
27 a maximum of 4 devices can be addressed on a single bus. Hence the value of
28 this property should be 1.
29 - #size-cells: Should be 0. There are cases where it makes sense to use a
30 different value here. See below.
31
32 Optional properties:
33 - clock-master: boolean. Should be enabled if the host is being used in
34 conjunction with another DSI host to drive the same peripheral. Hardware
35 supporting such a configuration generally requires the data on both the busses
36 to be driven by the same clock. Only the DSI host instance controlling this
37 clock should contain this property.
38
39 DSI peripheral
40 ==============
41
42 Peripherals with DSI as control bus, or no control bus
43 ------------------------------------------------------
44
45 Peripherals with the DSI bus as the primary control bus, or peripherals with
46 no control bus but use the DSI bus to transmit pixel data are represented
47 as child nodes of the DSI host's node. Properties described here apply to all
48 DSI peripherals, but individual bindings may want to define additional,
49 device-specific properties.
50
51 Required properties:
52 - reg: The virtual channel number of a DSI peripheral. Must be in the range
53 from 0 to 3.
54
55 Some DSI peripherals respond to more than a single virtual channel. In that
56 case two alternative representations can be chosen:
57 - The reg property can take multiple entries, one for each virtual channel
58 that the peripheral responds to.
59 - If the virtual channels that a peripheral responds to are consecutive, the
60 #size-cells can be set to 1. The first cell of each entry in the reg
61 property is the number of the first virtual channel and the second cell is
62 the number of consecutive virtual channels.
63
64 Peripherals with a different control bus
65 ----------------------------------------
66
67 There are peripherals that have I2C/SPI (or some other non-DSI bus) as the
68 primary control bus, but are also connected to a DSI bus (mostly for the data
69 path). Connections between such peripherals and a DSI host can be represented
70 using the graph bindings [1], [2].
71
72 Peripherals that support dual channel DSI
73 -----------------------------------------
74
75 Peripherals with higher bandwidth requirements can be connected to 2 DSI
76 busses. Each DSI bus/channel drives some portion of the pixel data (generally
77 left/right half of each line of the display, or even/odd lines of the display).
78 The graph bindings should be used to represent the multiple DSI busses that are
79 connected to this peripheral. Each DSI host's output endpoint can be linked to
80 an input endpoint of the DSI peripheral.
81
82 [1] Documentation/devicetree/bindings/graph.txt
83 [2] Documentation/devicetree/bindings/media/video-interfaces.txt
84
85 Examples
86 ========
87 - (1), (2) and (3) are examples of a DSI host and peripheral on the DSI bus
88 with different virtual channel configurations.
89 - (4) is an example of a peripheral on a I2C control bus connected to a
90 DSI host using of-graph bindings.
91 - (5) is an example of 2 DSI hosts driving a dual-channel DSI peripheral,
92 which uses I2C as its primary control bus.
93
94 1)
95 dsi-host {
96 ...
97
98 #address-cells = <1>;
99 #size-cells = <0>;
100
101 /* peripheral responds to virtual channel 0 */
102 peripheral@0 {
103 compatible = "...";
104 reg = <0>;
105 };
106
107 ...
108 };
109
110 2)
111 dsi-host {
112 ...
113
114 #address-cells = <1>;
115 #size-cells = <0>;
116
117 /* peripheral responds to virtual channels 0 and 2 */
118 peripheral@0 {
119 compatible = "...";
120 reg = <0, 2>;
121 };
122
123 ...
124 };
125
126 3)
127 dsi-host {
128 ...
129
130 #address-cells = <1>;
131 #size-cells = <1>;
132
133 /* peripheral responds to virtual channels 1, 2 and 3 */
134 peripheral@1 {
135 compatible = "...";
136 reg = <1 3>;
137 };
138
139 ...
140 };
141
142 4)
143 i2c-host {
144 ...
145
146 dsi-bridge@35 {
147 compatible = "...";
148 reg = <0x35>;
149
150 ports {
151 ...
152
153 port {
154 bridge_mipi_in: endpoint {
155 remote-endpoint = <&host_mipi_out>;
156 };
157 };
158 };
159 };
160 };
161
162 dsi-host {
163 ...
164
165 ports {
166 ...
167
168 port {
169 host_mipi_out: endpoint {
170 remote-endpoint = <&bridge_mipi_in>;
171 };
172 };
173 };
174 };
175
176 5)
177 i2c-host {
178 dsi-bridge@35 {
179 compatible = "...";
180 reg = <0x35>;
181
182 ports {
183 #address-cells = <1>;
184 #size-cells = <0>;
185
186 port@0 {
187 reg = <0>;
188 dsi0_in: endpoint {
189 remote-endpoint = <&dsi0_out>;
190 };
191 };
192
193 port@1 {
194 reg = <1>;
195 dsi1_in: endpoint {
196 remote-endpoint = <&dsi1_out>;
197 };
198 };
199 };
200 };
201 };
202
203 dsi0-host {
204 ...
205
206 /*
207 * this DSI instance drives the clock for both the host
208 * controllers
209 */
210 clock-master;
211
212 ports {
213 ...
214
215 port {
216 dsi0_out: endpoint {
217 remote-endpoint = <&dsi0_in>;
218 };
219 };
220 };
221 };
222
223 dsi1-host {
224 ...
225
226 ports {
227 ...
228
229 port {
230 dsi1_out: endpoint {
231 remote-endpoint = <&dsi1_in>;
232 };
233 };
234 };
235 };
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