BBB LCD3 Backlight Problem in Android


I’m using LCD3 with BBB, which runs on Android. But I have no control on backlight. I’m trying to change backlight via adb:

echo 100 > /sys/class/backlight/tps65217-bl/brightness

But nothing happens. When I try to change brightness in Android settings, I can see the change in /sys/class/backlight/tps65217-bl/brightness via cat /sys/class/backlight/tps65217-bl/brightness . But it doesn’t work either. What should I do?