Display link bug with alsa and pulseaudio

[ppr]

I notice a bug occurring after the installation of displaylink on Linux.

I had three shortcuts related to audio control using alsa (and pulseaudio) (bounded to different keystrokes)

amixer -q -D pulse set Master 5%- unmute -> Ctrl+PgUp
amixer -q -D pulse set Master 5%+ unmute -> Ctrl+PgDn
amixer -q -D pulse set Master toggle -> Ctrl+M

I recently purchase a Dell D3000 ports replicator and install displaylink to use it at its best (I didn't try but I read only Ethernet and USB ports are working without displaylink software on Linux and the HDMI output needed this software).

Anyway, the ports replicator and displaylink work well but my three alsa shortcuts are not working after displaylink installation. I have this error message when trying the shorcuts in a terminal:

$ amixer -q -D pulse set Master toggle
ALSA lib control.c:954:(snd_ctl_open_noupdate) Invalid CTL pulse
amixer: Mixer attach pulse error: No such file or directory

I have two exact same laptop (Dell Latitude 6430U) with same software version. I tested on my second laptop: The shortcuts were working, I installed displaylink and they weren't anymore. So I'm sure this is a bug related to displaylink driver for Linux.

I tried to uninstalled displaylink but the alsa shortcuts are not working back.

I am available to provide logs and to test some manipulations if needed.

[mlukaszek]

Someone else will probably be able to help here. The key will probably be the fact that after connecting the docking station (regardless of the fact if you installed the drivers or not), you will essentially have a second audio device in the system, that's driven by usbaudio - and this will be true until you rebooted with no device connected. Therefore, some extra magic might be required for amixer/pulse to know what your intentions are.

Regards,
Michal