ok, I've managed to sort this out on my own. I've decompiled the rockchip-rockpi4.dtb and find out that pwm is disabled by default. So I've wrote new overlay for pwm, just to enable it :
/dts-v1/;
/ {
compatible = "rockchip,rk3399";
fragment@0 {
target-path = "/aliases";
__overlay__ {
pwm0 = "/pwm@ff420000";
pwm1 = "/pwm@ff420010";
};
};
fragment@1 {
target-path = "/pwm@ff420000";
__overlay__ {
status = "okay";
};
};
fragment@2 {
target-path = "/pwm@ff420010";
__overlay__ {
status = "okay";
};
};
};
next, compiled it with dtc :
dtc -O dtb -o rockchip-pwm-gpio.dtbo -b 0 -@ rockchip-pwm-gpio.dts
and moved dtbo to /boot/dtc/rockchip/overlays, and activated it in overlays in /boot/armbianEnv.txt.
Now PWM works like a charm. I'm just leaving this thread and my resolution as reference, for anyone with the same problem.
