Hi Takashi,
I notice you are doing a lot of cleanups to HDA code. Just FYI I'm looking into modifying the SOF Intel backend to use snd-hda-codec-hdmi/patch_hdmi.c for HDMI/DP audio support, i.e. to be able to share this code between snd-hda-intel and SOF Intel (and not using hdac-hdmi).
Let me know if this clashes with something you are already looking into. I have a very rough version up and running, but it still needs some work. If the general idea seems ok to you, I'll continue to work on a RFC patch and send for review.
This will change how HDMI is exposed to user-space with SOF Intel drivers, so we need to be extra careful how this is introduced. But this really seems to be the best way to go to avoid the duplicated maintenance work with two drivers that we now have.
PS Tracked in SOF github as https://github.com/thesofproject/linux/issues/1123
Br, Kai