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= Linux Backlight class digital display backlights =
A digital display which has a backlight may have a Linux backlight driver which provides a sysfs API. Typically these are implemented via PWM signals allowing a variable brightness or a GPIO signal allowing a simple on/off.

Mapping A backlight driver to a PWM, GPIO, or other controller is done in the board support file or in the case of more modern kernels such as Ventana in the device-tree. See the backlight node in the [http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/imx6qdl-gw54xx.dtsi#n31 ​gw54xx device-tree] for example.

To list available backlight controllers:
{{{#!bash
ls /sys/class/backlight
}}}

To see current/available brightness values:
{{{#!bash
cat /sys/class/backlight/*/brightness # current brightness
cat /sys/class/backlight/*/max_brightness # max brightness
}}}

To set brightness (to a value equal or less than max_brightness)
{{{#!bash
echo 0 > /sys/class/backlight/*/brightness # turn off backlight
}}}

References:
 * ​[http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.txt GPIO backlight]
 * [http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt PWM backlight]
 * [http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/stable/sysfs-class-backlight sysfs-class-backlight]

= Other References =
Here are some other useful references from our wiki:
* [wiki:gpio General Purpose I/O (GPIO)]
* [wiki:linux/pwm Pulse-Width-Modulation (PWM)]
* [wiki:OpenWrt/gpio GPIO in OpenWrt]
* [wiki:ventana/DigitalIO Ventana product family Digital I/O]