Common Properties for Display Panel
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===================================
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This document defines device tree properties common to several classes of
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display panels. It doesn't constitue a device tree binding specification by
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itself but is meant to be referenced by device tree bindings.
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When referenced from panel device tree bindings the properties defined in this
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document are defined as follows. The panel device tree bindings are
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responsible for defining whether each property is required or optional.
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Descriptive Properties
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----------------------
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- width-mm,
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- height-mm: The width-mm and height-mm specify the width and height of the
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physical area where images are displayed. These properties are expressed in
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millimeters and rounded to the closest unit.
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- label: The label property specifies a symbolic name for the panel as a
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string suitable for use by humans. It typically contains a name inscribed on
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the system (e.g. as an affixed label) or specified in the system's
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documentation (e.g. in the user's manual).
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If no such name exists, and unless the property is mandatory according to
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device tree bindings, it shall rather be omitted than constructed of
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non-descriptive information. For instance an LCD panel in a system that
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contains a single panel shall not be labelled "LCD" if that name is not
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inscribed on the system or used in a descriptive fashion in system
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documentation.
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Display Timings
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---------------
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- panel-timing: Most display panels are restricted to a single resolution and
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require specific display timings. The panel-timing subnode expresses those
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timings as specified in the timing subnode section of the display timing
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bindings defined in
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Documentation/devicetree/bindings/display/panel/display-timing.txt.
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Connectivity
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------------
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- ports: Panels receive video data through one or multiple connections. While
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the nature of those connections is specific to the panel type, the
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connectivity is expressed in a standard fashion using ports as specified in
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the device graph bindings defined in
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Documentation/devicetree/bindings/graph.txt.
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- ddc-i2c-bus: Some panels expose EDID information through an I2C-compatible
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bus such as DDC2 or E-DDC. For such panels the ddc-i2c-bus contains a
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phandle to the system I2C controller connected to that bus.
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Control I/Os
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------------
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Many display panels can be controlled through pins driven by GPIOs. The nature
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and timing of those control signals are device-specific and left for panel
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device tree bindings to specify. The following GPIO specifiers can however be
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used for panels that implement compatible control signals.
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- enable-gpios: Specifier for a GPIO connected to the panel enable control
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signal. The enable signal is active high and enables operation of the panel.
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This property can also be used for panels implementing an active low power
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down signal, which is a negated version of the enable signal. Active low
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enable signals (or active high power down signals) can be supported by
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inverting the GPIO specifier polarity flag.
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Note that the enable signal control panel operation only and must not be
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confused with a backlight enable signal.
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- reset-gpios: Specifier for a GPIO coonnected to the panel reset control
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signal. The reset signal is active low and resets the panel internal logic
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while active. Active high reset signals can be supported by inverting the
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GPIO specifier polarity flag.
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Power
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-----
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- power-supply: display panels require power to be supplied. While several
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panels need more than one power supply with panel-specific constraints
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governing the order and timings of the power supplies, in many cases a single
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power supply is sufficient, either because the panel has a single power rail,
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or because all its power rails can be driven by the same supply. In that case
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the power-supply property specifies the supply powering the panel as a phandle
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to a regulator.
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Backlight
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---------
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Most display panels include a backlight. Some of them also include a backlight
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controller exposed through a control bus such as I2C or DSI. Others expose
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backlight control through GPIO, PWM or other signals connected to an external
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backlight controller.
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- backlight: For panels whose backlight is controlled by an external backlight
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controller, this property contains a phandle that references the controller.
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