Please bear with me, I am brand new to Linux and RetroArch.
I have a generic PS3 controller, wireless "AfterGlow" with a USB dongle, that I want to use on RetroArch. In spite of my various attempts RetroArch has failed to detect any inputs from the controller, yes it's on and yes it's fully charged (AA battery powered). I am running Ubuntu 18.04 on my laptop. All USB ports are operating. Bluetooth is enabled and functioning properly. Other input devices are all functioning (keyboard, touchscreen, touchpad, wireless mouse with USB dongle).