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1 | Common Properties for Display Panel |
2 | =================================== | |
3 | ||
4 | This document defines device tree properties common to several classes of | |
5 | display panels. It doesn't constitue a device tree binding specification by | |
6 | itself but is meant to be referenced by device tree bindings. | |
7 | ||
8 | When referenced from panel device tree bindings the properties defined in this | |
9 | document are defined as follows. The panel device tree bindings are | |
10 | responsible for defining whether each property is required or optional. | |
11 | ||
12 | ||
13 | Descriptive Properties | |
14 | ---------------------- | |
15 | ||
16 | - width-mm, | |
17 | - height-mm: The width-mm and height-mm specify the width and height of the | |
18 | physical area where images are displayed. These properties are expressed in | |
19 | millimeters and rounded to the closest unit. | |
20 | ||
21 | - label: The label property specifies a symbolic name for the panel as a | |
22 | string suitable for use by humans. It typically contains a name inscribed on | |
23 | the system (e.g. as an affixed label) or specified in the system's | |
24 | documentation (e.g. in the user's manual). | |
25 | ||
26 | If no such name exists, and unless the property is mandatory according to | |
27 | device tree bindings, it shall rather be omitted than constructed of | |
28 | non-descriptive information. For instance an LCD panel in a system that | |
29 | contains a single panel shall not be labelled "LCD" if that name is not | |
30 | inscribed on the system or used in a descriptive fashion in system | |
31 | documentation. | |
32 | ||
33 | ||
34 | Display Timings | |
35 | --------------- | |
36 | ||
37 | - panel-timing: Most display panels are restricted to a single resolution and | |
38 | require specific display timings. The panel-timing subnode expresses those | |
39 | timings as specified in the timing subnode section of the display timing | |
40 | bindings defined in | |
f1303070 | 41 | Documentation/devicetree/bindings/display/panel/display-timing.txt. |
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42 | |
43 | ||
44 | Connectivity | |
45 | ------------ | |
46 | ||
47 | - ports: Panels receive video data through one or multiple connections. While | |
48 | the nature of those connections is specific to the panel type, the | |
49 | connectivity is expressed in a standard fashion using ports as specified in | |
50 | the device graph bindings defined in | |
51 | Documentation/devicetree/bindings/graph.txt. | |
52 | ||
53 | - ddc-i2c-bus: Some panels expose EDID information through an I2C-compatible | |
54 | bus such as DDC2 or E-DDC. For such panels the ddc-i2c-bus contains a | |
55 | phandle to the system I2C controller connected to that bus. | |
56 | ||
57 | ||
58 | Control I/Os | |
59 | ------------ | |
60 | ||
61 | Many display panels can be controlled through pins driven by GPIOs. The nature | |
62 | and timing of those control signals are device-specific and left for panel | |
63 | device tree bindings to specify. The following GPIO specifiers can however be | |
64 | used for panels that implement compatible control signals. | |
65 | ||
66 | - enable-gpios: Specifier for a GPIO connected to the panel enable control | |
67 | signal. The enable signal is active high and enables operation of the panel. | |
68 | This property can also be used for panels implementing an active low power | |
69 | down signal, which is a negated version of the enable signal. Active low | |
70 | enable signals (or active high power down signals) can be supported by | |
71 | inverting the GPIO specifier polarity flag. | |
72 | ||
73 | Note that the enable signal control panel operation only and must not be | |
74 | confused with a backlight enable signal. | |
75 | ||
76 | - reset-gpios: Specifier for a GPIO coonnected to the panel reset control | |
77 | signal. The reset signal is active low and resets the panel internal logic | |
78 | while active. Active high reset signals can be supported by inverting the | |
79 | GPIO specifier polarity flag. | |
80 | ||
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81 | Power |
82 | ----- | |
83 | ||
84 | - power-supply: display panels require power to be supplied. While several | |
85 | panels need more than one power supply with panel-specific constraints | |
86 | governing the order and timings of the power supplies, in many cases a single | |
87 | power supply is sufficient, either because the panel has a single power rail, | |
88 | or because all its power rails can be driven by the same supply. In that case | |
89 | the power-supply property specifies the supply powering the panel as a phandle | |
90 | to a regulator. | |
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91 | |
92 | Backlight | |
93 | --------- | |
94 | ||
95 | Most display panels include a backlight. Some of them also include a backlight | |
96 | controller exposed through a control bus such as I2C or DSI. Others expose | |
97 | backlight control through GPIO, PWM or other signals connected to an external | |
98 | backlight controller. | |
99 | ||
100 | - backlight: For panels whose backlight is controlled by an external backlight | |
101 | controller, this property contains a phandle that references the controller. |