I appear to have the same issue as:
root@ML-A8FE:~# amixer --card tegrahda controls
numid=1,iface=CARD,name=‘HDMI/DP,pcm=3 Jack’
numid=12,iface=CARD,name=‘HDMI/DP,pcm=7 Jack’
numid=8,iface=MIXER,name=‘d HDA Comfort Noise’
numid=6,iface=MIXER,name=‘d HDA Decode Capability’
numid=7,iface=MIXER,name=‘d HDA Maximum PCM Channels’
numid=2,iface=MIXER,name=‘d IEC958 Playback Con Mask’
numid=4,iface=MIXER,name=‘d IEC958 Playback Default’
numid=3,iface=MIXER,name=‘d IEC958 Playback Pro Mask’
numid=5,iface=MIXER,name=‘d IEC958 Playback Switch’
numid=19,iface=MIXER,name=‘h HDA Comfort Noise’
numid=17,iface=MIXER,name=‘h HDA Decode Capability’
numid=18,iface=MIXER,name=‘h HDA Maximum PCM Channels’
numid=13,iface=MIXER,name=‘h IEC958 Playback Con Mask’
numid=15,iface=MIXER,name=‘h IEC958 Playback Default’
numid=14,iface=MIXER,name=‘h IEC958 Playback Pro Mask’
numid=16,iface=MIXER,name=‘h IEC958 Playback Switch’
numid=10,iface=MIXER,name=‘d HDA Custom ELD’,device=2
numid=21,iface=MIXER,name=‘h HDA Custom ELD’,device=2
numid=11,iface=PCM,name=‘Playback Channel Map’,device=3
numid=9,iface=PCM,name=‘d ELD’,device=3
numid=22,iface=PCM,name=‘Playback Channel Map’,device=7
numid=20,iface=PCM,name=‘h ELD’,device=7
root@ML-A8FE:~# amixer --card tegrahda sget “h IEC958”
Simple mixer control ‘h IEC958’,0
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [on]
root@ML-A8FE:~# amixer --card tegrahda sget “d IEC958”
Simple mixer control ‘d IEC958’,0
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [on]
But have no sound at the monitor/speakers. The hardware has previously worked with R28.2.1 based distribution on it. I am using the yocto based tegrademo distro on it, but based on the above it appears it should work.