ok, found it here http://wiki.friendlyarm.com/wiki/index.php/FriendlyThings_for_RK3399#PWM in short APIs for Accessing PWM Export PWM0 to users echo 0 > /sys/class/pwm/pwmchip1/export Control a PWM fan's speed by setting the PWM's period and duty_cycle. echo 0 > /sys/class/pwm/pwmchip1/pwm0/enable e...