| bl_power | brightness | BL_ON |
|---|---|---|
| 1 | don't care | 0 |
| 0 | 0 | 0 |
| 0 | 1..max_brightness | 1 |
Note that the Apalis/Colibri iMX6 V2.7 Beta 1 and earlier did not control BL_ON at all.
boot2qt / meta-ujet / recipes-kernel / linux / linux-toradex-4.1-2.0.x / apalis-imx6 / fix-ixora-dts.patch
154 -#endif
155 - brightness-levels = <0 4 8 16 32 64 128 255>;
156 - default-brightness-level = <6>;
157 - status = "okay";
The files bl_power and brightness in /sys/class/backlight/backlight/ control the PWM signal.
The device tree contains the backlight configuration. This includes a mapping of brightness values to duty cycles with the value 0 generating a duty cycle of 0% and the value in max_brightness generating a duty cycle of 100%. Also the PWM frequency and polarity can be configured.
The following queries the number of brightness steps, sets the duty cycle to brightest and then to its darkest.
# cat /sys/class/backlight/backlight/max_brightness
7
# echo 7 > /sys/class/backlight/backlight/brightness
# echo 1 > /sys/class/backlight/backlight/brightness
| 0 | Off |
|---|---|
| 1 | brightest |
| 2 | normal bright |
| 3 | normal bright |
| 4 | normal bright |
| 5 | normal bright |
| 6 | darkest |
| 7 | Off |
The following can be used to switch the duty cycle to 0% and back to the level determined by what is in the brightness file.
# echo 1 > /sys/class/backlight/backlight/bl_power
# echo 0 > /sys/class/backlight/backlight/bl_power
| BL_POWER | Meaning |
|---|---|
| 0 | ON |
| 1 | OFF |
The device tree also allows to define the PWM polarity to adapt to displays with inverted brightness.
e.g.
diff --git a/arch/arm/boot/dts/vf-colibri.dtsi b/arch/arm/boot/dts/vf-colibri.dtsi
index 7c5e69e..c230ab5 100644
--- a/arch/arm/boot/dts/vf-colibri.dtsi
+++ b/arch/arm/boot/dts/vf-colibri.dtsi
@@ -14,7 +14,7 @@
bl: backlight {
compatible = "pwm-backlight";
- pwms = <&pwm0 0 5000000 0>;
+ pwms = <&pwm0 0 5000000 1>;
status = "disabled";
};
};
| actual_brightness | 6 |
|---|---|
| bl_power | 0 or 1 |
| brightness | 1 to 7 |
| max_brightness | 7 |
PWM (Linux) https://developer.toradex.com/knowledge-base/pwm-(linux\
Backlight (Linux) https://developer.toradex.com/knowledge-base/backlight-(linux\