Sound from HDMI (pcm2) using i915kms.ko

Steven Friedrich FreeBSD at
Mon Feb 15 18:11:47 UTC 2021

I am running FreeBSD 12.2-RELEASE-p3 FreeBSD 12.2-RELEASE-p3 r369261 FreeBSD  
I put hw.snd.default_unit=2 in /etc/sysctl.conf to make pcm2 default.
cat /dev/sndstat confirms:
Installed devices:
pcm0: <Realtek ALC671 (Rear Analog)> (play/rec)
pcm1: <Realtek ALC671 (Analog)> (play/rec)
pcm2: <Intel Kaby Lake (HDMI/DP 8ch)> (play) default
No devices installed from userspace.

But no sound is emitted from HDMI connector.

It's my understanding that this requires some support in the video driver, 

I have added WITHOUT_MODULES=i915kms
to /etc/make.conf, and built from ports, both:
drm-fbsd12.0-kmod-4.16.g20201016_1 DRM modules for the linuxkpi-based KMS 
gpu-firmware-kmod-g20201213    Firmware modules for the linuxkpi-based KMS 
Still no joy.
My processor is: Core i7-8700 (Coffee Lake), with UHD Graphics 630.

I also tried tunable: hw.snd.compat_linux_mmap=1 in /etc/sysctl.conf, to no 
I get sound under Linux Mint, KDE Neon, Kubuntu, and Windows 10 Pro.
I do get sound from pcm0(rear audio jack) or pcm1(front audio jack).
But this monitor is shared with a Windows machine and FreeBSD is the only OS 
not outputting sound on HDMI.

Any ideas?

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