Re: [PATCH v3] ALSA: usb-audio: Skip broken playback feature unit on XiiSound chips

[Takashi Iwai <tiwai@suse.de>]

On Sat, 07 Nov 2026 03:26:43 +0100,
Cristiano Souza wrote:
> 
> Weltrend XiiSound-based devices (040b:0897, e.g. Redragon H878
> wireless headset) expose a UAC1 playback feature unit whose volume
> and mute controls are unusable in practice: the reported per-channel
> dB range is only 0..+0.39dB, yet setting any volume below the
> maximum mutes one or even both channels, and the mapping between
> logical and physical channels is unreliable.  Any attempt by
> userspace to drive the hardware volume therefore results in muted
> or one-sided audio.
> 
> Ignore the playback feature unit via a usbmix_name_map so that
> userspace falls back to software volume, and pin the unit's master
> and per-channel volumes to the reported maximum with mutes cleared
> when the mixer is created, so the signal path always stays fully
> open.  The capture path (microphone feature unit) is not affected
> and keeps working.
> 
> Tested with a Redragon H878 wireless headset on PipeWire/PulseAudio:
> stereo output works on both channels at any volume, software volume
> applies smoothly, and mute/unmute works.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Cristiano Souza <cristianocps@gmail.com>

Applied to for-next branch.  Thanks.


Takashi