audiohd ignores digital output pins such as HDMI/DP
The audiohd driver currently makes no attempt to drive digital output pins that are associated with HDMI or DisplayPort devices.
Updated by Hans Rosenfeld about 3 years ago
One of the problems with the audiohd driver is that it needs to know how many channels there are at attach time. This is normally true for any other audiohd device, but in case of HDMI/DP that can change any time when a user plugs in a display. This change uses a simple approach to make this work in 2-channel mode only. I don't have any other hardware to test so there isn't really much of a point in trying to support anything else right now.
While code is there to get the EDID-like data from the attached display when it is plugged in, nothing is really done with this data yet. It proved to be helpful for debugging this and will be useful for extending this to support devices with more channels, and perhaps also to make this more dynamic.
I have tested this with a nVIDIA GTX 1080 only due to lack of other hardware. It works on both HDMI and DP outputs and keeps working when plugging the display cable into a different connector while audio is playing. Of course, DPMS power-off will also turn off audio output, but there is little that can be done here. I've also verified that it doesn't break "regular" audiohd output (on my ThinkPad).