Looks like no progress has been made on this kernel issue over on the Github issue by the Raspberry Pi developers.
However a couple of observations - there is at least one report in that thread that the same USB audio dropout/glitch issue exists on x86 on 4.x kernels on USB 2 ports…
Also in the volumio 2 for cubox-i thread gkkpch is working on a Cubox-i build of Volumio using a 4.x (Armbian ?) kernel - and is also experiencing USB audio glitches and dropouts.
As I experience zero USB audio glitches on the current build of Volumio for Cubox-i which is based on a 3.14 kernel, it has got me thinking - is my Cubox-i only avoiding this issue because it is still on an old 3.14 kernel, and could this be a more generic problem with USB audio in 4.x kernels that can manifest on more than just the Raspberry Pi or even more than just arm ?
To test this theory, is there any easy way to get a test build of Volumio for Raspberry Pi 2 which is identical to the current stable version except for using a 3.14 kernel ? That would be very interesting to see if the glitches remain or not, and may help narrow down whether this is really a Pi problem or a more general 4.x kernel problem.
When the 4.x kernel series first came out I remember there were many nasty regressions on both Pi and Cubox-i that took a long while to be resolved.
I’ve offered for gkkpch to try our heavily patched OSMC 4.4.0 kernel sources for Cubox-i to see if this helps with the USB audio glitches, but I’m starting to wonder if that will actually help if its a more general 4.x kernel problem! (Unless one of our many patches does actually address it. There are so many I’m not sure)