(In reply to comment #10)
> (In reply to comment #9)
> > (b) Can you test out a 3.7-based kernel?
> I suppose I can.  Let me know if it's critical for you to proceed with your
> work.  I'd rather wait for some more of your thoughts/tests/results _if
> possible_.  However, I'll jump to it immediately if you say the word.

Well, the situation is that I don't have any HDMI devices at all (either with
HDMI outputs or inputs, forget HDMI audio), nor do I know anything about it. So
if this doesn't work, that means that someone else needs to (a) reproduce your
issue [and note, hdmi audio does work for some other people, so there must be
something a bit more special about your situation, be it EDID data or more
missed register setup], and (b) do the RE work to figure out what we're
missing.

It seems like testing out an old kernel is easy by comparison. However I don't
hold out a huge amount of hope for it, since like you said, eld_valid = 0,
which more likely indicates an EDID issue.

If you're interested, some minor code inspection shows that at least some of
the logic is in nv50_display.c:nv50_audio_mode_set. You could add prints in
there to see what it's detecting stuff as. You could also add prints to
drm_edid.c:drm_detect_monitor_audio, perhaps your monitor's EDID is different
than what it expects.

Looks like there are a few prints already, you could see what happens when you
boot with drm.debug=0x06 which should output nouveau- and kms-related debug
statements.