Comment 30 for bug 1540372

Don't create "Analog Loopback" controls as default since these controls are usually more harmful than useful for normal users. Only created when "loopback = yes" hint is given.

You have to enable loopback by hint loopback=true using early patching

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/tree/Documentation/sound/alsa/HD-Audio.txt