Comment 24 for bug 1834771

I started to experience this same issue with Ubuntu 16.04. I performed an apt upgrade and after rebooting I did not have any sound from my HDMI port.

I did some research and I think I figured out why my Ubuntu 16.04 machine would not output audio on an HDMI port. I believe this is the same issue the original poster was experiencing.

There was a patch added to the kernel on 20 May 2019:
https://<email address hidden>/

My understanding is that sometimes HDMI ports where reported as plugged in even though they were not. To fix this the patch added a line of code that takes into account the eld_valid value along with the monitor_present value located at /proc/asound/cardX/eld#N.M.

When I cat /proc/asound/card1/eld* I see monitor_present is 1 but eld_valid is 0 so this new line of code in hdmi_present_sense_via_verbs() will set jack->pin_sense to 0 instead of AC_PINSENSE_PRESENCE. That must cause the HDMI audio to appear unplugged.

I further tested this theory by booting kernel 4.15.0-50 and now my HDMI audio works. If I boot back to 4.15.0-54 the HDMI audio reports unplugged and I do not get any audio on the HDMI cable.

My understanding is that a video driver is responsible for setting eld_valid and my Radeon driver must not be doing that. So either the patch needs to be undone or the video drivers need to be patched. Otherwise we cannot use any kernels after 4.15.0-50.