Well. Gamepad just doesn't work. I can't see how this is a "proper" Linux port.
Currently suggested hack is xf86-input-joystick, which is just a hack to control keyboard/mouse using a joystick. In case you're not familiar with GNU/Linux, no, this is not having gamepad support in GNU/Linux userland.
Please 1) either remove the misleading information on your store page (that is, do not advertise your product as having gamepad support or having proper Linux support) 2) or fix the gamepad code.