@Lazar-Demin I'm really glad about the open source LEDE tree! Thanks! As I am just on my way to vacation right now, I can't dig deep into it right now But regarding PWM, the only thing that seems missing (I couldn't actually test, just compared my tree / .config with yours) is actually enabling it in the device tree. I had to append &pwm { status = "okay"; }; at the end of target/linux/ramips/dts/OMEGA2.dtsi to make the /sys/class/pwm interface work for me with kernel 4.4 (lede-17.01), so it should work for the Onion FW build. With kernel 4.9 however, (LEDE master) there seems to be some resource conflict over GPIO18 and 19, which makes the PWM driver fail at load. Couldn't find out details yet.

@Zheng-Han This makes a bit more sense. However: I note that the picture of the physical switch actually shows a fifth solder connection - between 1 & 2 in your picture - and I observe that this is soldered on my Expansion Dock I still don't understand just how this all works and how the switch is actually connected. @Lazar-Demin above says that the RESET_BTN is connected to ground when the button is NOT depressed. I still don't see how this works given the circuit diagram and your description of the button