Plug your controller setup in your Pi without any other controller except the keyboard, boot it up, close ES and run thisls /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 withlsusb
If a controller is present and you want to test if the device translates the PS2 buttons correctly, run this and testjstest /dev/input/jsX