[Bug 1921452] Re: [SRU] alsa-lib: conf: USB - add "Cmedia Audio" to USB-Audio.pcm.iec958_device

Sebastien Bacher 1921452 at bugs.launchpad.net
Tue Apr 6 19:29:03 UTC 2021

Uploaded to 20.10 also, there was another SRU done in novembre though,
please try to base your changes on the current version, the debdiff
didn't apply to that version since it was done on top of the release
pocket version instead

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  [SRU] alsa-lib: conf: USB - add "Cmedia Audio" to USB-

Status in OEM Priority Project:
  In Progress
Status in alsa-lib package in Ubuntu:
  Fix Released
Status in alsa-lib source package in Focal:
  In Progress
Status in alsa-lib source package in Groovy:
  In Progress
Status in alsa-lib source package in Hirsute:
  Fix Released

Bug description:
  On Cmedia Audio, unusable SPDIF can be selected as output from PulseAudio.

  Disable IEC958 (SPDIF) through ALSA UCM.

  With the UCM applied, `pactl` and audio panel in gnome-control-center no longer have SPDIF option.

  [Where problems will occur]
  "Cmedia Audio" is the sound card name of this usb audio dongle, and this string is got from usb string descriptor, that is to say the "Cmedia Audio" is hard-coded in the firmware of that usb dongle.
  Not all Cmedia usb audio dongle use "Cmedia Audio", most of the dongles don't set string descriptor, then the audio driver sets a generic name "USB Audio Device" for them, if a dongle has string descriptor, it may have different string like "C-Media USB Headphone Set", and all dongles I met before don't have SPDIF interface.
  So If this SRU could introduce regression, it will happen on a Cmedia usb audio dongle which also hard-codes the "Cmedia Audio" in the string descriptor and it has SPDIF interface on it, after this SRU, users couldn't find the SPDIF playback device from the gnome-sound-setting. But this regression chance is very low since it is very rare a cmedia usb audio dongle uses "Cmedia Audio" in the string descriptor and it is very rare a usb audio dongle has SPDIF interface. So far we haven't met such a cmedia usb audio dongle.

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