This bug was fixed in the package alsa-lib - 1.2.2-2.1ubuntu2.4
---------------
alsa-lib (1.2.2-2.1ubuntu2.4) focal; urgency=medium
* d/p/0001-conf-USB-add-Cmedia-Audio-to-USB-Audio.pcm.iec958_de.patch:
conf: USB - add "Cmedia Audio" to USB-Audio.pcm.iec958_device
(LP: #1921452)
-- Shengyao Xue <shengyao....@canonical.com> Tue, 06 Apr 2021 21:33:31
+0200
** Changed in: alsa-lib (Ubuntu Focal)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1921452
Title:
[SRU] alsa-lib: conf: USB - add "Cmedia Audio" to USB-
Audio.pcm.iec958_device
Status in OEM Priority Project:
Fix Released
Status in alsa-lib package in Ubuntu:
Fix Released
Status in alsa-lib source package in Focal:
Fix Released
Status in alsa-lib source package in Groovy:
Fix Released
Status in alsa-lib source package in Hirsute:
Fix Released
Bug description:
[Impact]
On Cmedia Audio, unusable SPDIF can be selected as output from PulseAudio.
[Fix]
Disable IEC958 (SPDIF) through ALSA UCM.
[Test]
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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