Matthias Reichl wrote:

Userspace expects to see a HDMI pcm, so remove the somewhat broken front and iec958 pcms and add a proper hdmi pcm instead.

The hdmi pcm supports HD/HBR audio passthrough and relays the IEC958 status bits on to the kernel driver so it can switch to HBR audio packets if needed. The control hook is marked optional because kernels before 5.14 didn't expose the IEC958 controls.

The default pcm never worked as dmix doesn't support the iec958 format. So drop dmix, only use plug and softvol, and use the hdmi pcm for iec958 formatting.

I can confirm the upstream cards/vc4-hdmi.conf is not usable, and RPiOS ships a patched version (which was an earlier version of this patch).

I've tested this version with RPiOS bullseye and all seems good. I could play stereo and multi-channel PCM from VLC. I could also play DTS, DTS-HD and TrueHD formats as passthrough using kodi.

It would be good if we can switch from a custom version of vc4-hdmi.conf to an upstream version in RPiOS when this is merged.

Tested-by: Dom Cobley popcornmix@gmail.com