Re: [PATCH] ALSA: usb-audio: Add quirk flags for AlphaTheta EUPHONIA

[Takashi Iwai]

On Sun, 03 May 2026 23:15:17 +0200,
Anton Swart wrote:
> 
> The AlphaTheta EUPHONIA (VID 0x2b73, PID 0x0047) is a USB Audio
> Class 2 DJ mixer that requires implicit feedback for full-duplex
> operation. The capture endpoint (0x83 IN, interface 2) acts as the
> implicit feedback source for the playback endpoint (0x03 OUT,
> interface 1), and the device firmware does not send isochronous
> data on the capture endpoint unless the host is simultaneously
> sending data on the playback endpoint, i.e. playback must be
> started first.
> 
> Without QUIRK_FLAG_PLAYBACK_FIRST the kernel waits for capture URBs
> before submitting playback URBs, creating a deadlock: the device
> waits for playback data and the host waits for capture data.
> Without QUIRK_FLAG_GENERIC_IMPLICIT_FB the kernel does not detect
> the implicit feedback relationship between the two interfaces.
> 
> The same flag combination is already used for the Behringer UMC202HD,
> UMC204HD and UMC404HD (0x1397:0x0507/0x0508/0x0509), which exhibit
> the identical implicit-feedback topology.
> 
> Tested on Raspberry Pi 5 with kernel 6.12.75; continuous full-duplex
> streaming at 96 kHz / 24-bit, zero XRUNs.
> 
> Signed-off-by: Anton Swart <anton.swart.jhb@xxxxxxxxx>

Applied now.  Thanks.


Takashi