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
echo 50000 > /sys/class/pwm/pwmchip1/pwm0/period
echo 1 > /sys/class/pwm/pwmchip1/pwm0/enable
echo 45000 > /sys/class/pwm/pwmchip1/pwm0/duty_cycle
I am running Armbian on my M4 and it works perfectly.