Plug your controller setup in your Pi without any other controller except the keyboard, boot it up, close ES and run this

ls /dev/input/

It should show all input devices of which joysticks/joypads are shown as jsX (eg. js0, js1, ...).

If it is not present, try to look if the USB device is present with

lsusb

If a controller is present and you want to test if the device translates the PS2 buttons correctly, run this and test

jstest /dev/input/jsX

By accident I found out that a Chrome OS computer is actually better than Windows 10 for setting up a Pi because it can read Linux filesystems, meaning I have access to both the boot and rootfs partitions. I also found a few remarkable Android apps for SSH and VNC. I did, however, need a Windows device for setup...

I'm currently new to making posts on these and am wondering about if someone has found a solution yet as of March 25th, 2019. Thank you all in advance!!

It seems that at least someone did it : http://www.synack.net/~bbraun/cabinet.html

I'm looking all through the code and have a tough time pin pointing where it is located. I'm not a big C++ guy but I'm decent at reading code.

This must be fairly easy for someone who is competent in C++, anyone else I'm certain I'm not the only person interested in this idea, maybe we can all work together...