Volume element has 4 channels. That's too much! I can't handle that!
Summary
We are prototyping some specialized USB sound card which consist of two 4-channels output. I have an issue with volume control. When I try to change volume e.g using pavucontrol, nothing happens(no USB requests for volume change). In Pulseaudio logs there is a warning: Volume element 'X' has 4 channels. That's too much! I can't handle that! I found that warning in alsa-mixer.c file. It seems that PCM element is limited to 2 channels only. Is the limit set for a reason?
environment
`uname -a`:
Linux localhost.localdomain 3.10.0-957.10.1.el7.x86_64 #1 SMP Mon Mar 18 15:06:45 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
`pulseaudio --version`:
pulseaudio 10.0
`amixer -c`:
Simple mixer control 'PCM',0 Capabilities: pvolume Playback channels: Front Left - Front Right - Rear Left - Rear Right Limits: Playback 0 - 338 Mono: Front Left: Playback 262 [78%] [9.07dB] Front Right: Playback 262 [78%] [9.07dB] Rear Left: Playback 295 [87%] [12.30dB] Rear Right: Playback 295 [87%] [12.30dB] Simple mixer control 'PCM',1 Capabilities: pvolume Playback channels: Front Left - Front Right - Rear Left - Rear Right Limits: Playback 0 - 338 Mono: Front Left: Playback 308 [91%] [13.57dB] Front Right: Playback 308 [91%] [13.57dB] Rear Left: Playback 239 [71%] [6.83dB] Rear Right: Playback 239 [71%] [6.83dB]
Steps to reproduce
Connect 4-channels PCM USB sound card and try to change volume using pavucontrol.
What is the current bug behavior?
No USB requests from host to change volume.
What is the expected correct behavior?
USB requests are sent to device.