Control user LEDs on Android


#1

Hello,

According to the DragonBoard’s hardware manual, two user LEDs are connected to APG GPIO 21 and APG GPIO 120, the other two are connected to PM PGIO 1 and PM GPIO 2.

How to I control them from user space, preferably through the same sysfs as documented in “GPIO Usage on Low Speed Connector Application Note”?

I tried to do:

  cd /sys/class/gpio
  export PIN=$((21 + 902))
  echo $PIN > export   # this failed

dmesg said:

  [69040.431307] _gpio_request: gpio-923 (sysfs) status -16
  [69040.431314] export_store: status -16

Apparently, these GPIO pins are not registered to the sysfs.


#2

Never mind, I found my answer. The apq8016-sbc.dtsi file declared the LEDs and these pins are controlled by led sybsystem instead of general gpio class.

For the interested readers:

  cd /sys/class/leds
  cd led1
  echo 1 > brightness  # turn on led 1
  echo 0 > brightness  # turn off