The title says most of the issue, but the critical issue is that I don't know why I can't find patch_cirrus.c. I was trying to solve the problem with Lunarts and friends, but what worked for them didn't work for me; i.e., adding the line:
options snd-hda-intel model=imac27_122,
to /etc/modprobe.p/alsa-base.conf, then, restarting the computer.

Does Lubuntu not have the file patch_cirrus.c?
How does it build the list of alsa options?

Please let me know if you need additional information.