The jstest-sdl package provides a program for testing gamepad/joystick inputs, which can help with mapping controllers manually as described in Mupen64Plus Components.
Install jstest-sdl by running the following commands:
sed -i 's/\-ltinfo//g' Makefile && make
Now, as the root
user:
install -v -m755 jstest-sdl /usr/bin/
sed -i 's/\-ltinfo//g' Makefile: This command avoids linking against an Ncurses library that wasn't built in LFS.