Re: [PATCH v2] ALSA: usb-audio: Add quirk for Shanling UP4

[Takashi Iwai <tiwai@suse.de>]

On Mon, 05 Oct 2026 14:59:53 +0200,
Vadym Shevchuk wrote:
> 
> The Shanling UP4 (0a12:1244, CSR-based, UAC1, full speed) sets the
> MaxPacketsOnly bit in its AS isochronous endpoint descriptor. With
> UAC_EP_CS_ATTR_FILL_MAX set, the driver fills every 1 ms packet up to
> wMaxPacketSize, i.e. 48 frames, regardless of the sample rate. At
> 44.1 kHz the device expects 44/45 frames per packet and outputs only
> silence. 48 kHz works because both packet sizes are the same there.
> 
> Measured with aplay on hw:UP4,0, 4 s of S16_LE stereo:
> 
>   before: 44.1 kHz consumed at ~48030 frames/s, done in 3.68 s, silent
>   after:  44.1 kHz consumed at ~44220 frames/s, done in 4.00 s, audible
> 
> 48 kHz plays fine both before and after the change. Regular music
> playback at 44.1 kHz through PipeWire sounds fine as well.
> 
> Clear the attribute for this device, as is already done for the MOTU
> MicroBook IIc. Since the packet sizes are equal at 48 kHz, this does
> not change anything for other devices that may share this CSR USB ID
> and only use 48 kHz.
> 
> Link: https://lore.kernel.org/all/CAPHAwzdUNRbZjBQuYKLf18EK_QGq0gR6Vx3YMZ=ffYKBogUtLA@mail.gmail.com/
> Signed-off-by: Vadym Shevchuk <0xsheff@gmail.com>

Applied to for-next branch now.  Thanks.


Takashi