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