alsaucm (part of the alsa-utils package) to set up the sound card:
ALSA_CONFIG_UCM=/opt/alsa/ucm alsaucm -c rk3399-gru-sound set _verb HiFi
Note that the port will display as "Headphones" despite using the speakers. When paired with pulseaudio and pulseaudio-alsa, be aware that the full volume range is addressed through levels 0-9 of the Master volume control. Levels 10-100 provide no additional gain.
If using pulseaudio, the following can be placed in your
~/.config/pulse/default.pa file to create a loopback device that fixes the volume levels, so that 0-100% in a desktop environment's volume bar will correspond to the audio level heard in the spaker.
.include /etc/pulse/default.pa load-module module-null-sink sink_name=corrected_speakers sink_properties=device.description=corrected_speakers load-module module-loopback source=corrected_speakers.monitor sink=alsa_output.platform-sound.stereo-fallback remix=false set-sink-volume alsa_output.platform-sound.stereo-fallback 6553 set-default-sink corrected_speakers
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