The annoying clicking when using Schiit DAC with TOSLink/COAX digital output from a Hifiberry Digi+ Pro

If one is using Hifiberry Digi+ Pro with the new VolumioNext build, one problem that might happen is that the digital output gets turned off in about 5 secs of idleness.

This is not ideal if your DAC uses a relay (Schiit Yggdrasil, NAD D5010, etc) and clicks like crazy when the signal switches off/on.

VolumioNext uses new kernel 4.9.31, so the changes in the driver for Digi+ Pro won't work. The new kernel introduces a new way of powering down the soc drivers in

sound/soc/soc-core.c

The module introduces a new parameter pmdown_time that can either be set during runtime or during boottime. I opted for boot-time, so adding

snd-soc-core.pmdown_time=-1

to the end of my /boot/cmdline.txt does the trick. Now my DAC locks onto the signal upon boot and only click when the player explicitly send rate change signals to the output, but that's another story.