Re: [BUG] ALSA: usb-audio: Shanling UP4 (0a12:1244) silent at 44.1 kHz due to MaxPacketsOnly

Re: [BUG] ALSA: usb-audio: Shanling UP4 (0a12:1244) silent at 44.1 kHz due to MaxPacketsOnly

[Takashi Iwai]

On Fri, 02 Oct 2026 11:17:51 +0200,
Vadym S wrote:
> 
> 
> Hello,
> 
> The Shanling UP4 (Bluetooth DAC/amp with a USB DAC mode; CSR-based,
> USB ID 0a12:1244, UAC1, full speed, S16_LE, 44100/48000 Hz) outputs
> silence at 44.1 kHz on Linux, while 48 kHz works. On Windows the same
> unit plays fine with the default format set to 16 bit / 44100 Hz.
> 
> The cause appears to be the MaxPacketsOnly bit in the class-specific
> AS isochronous endpoint descriptor (bmAttributes 0x81). snd-usb-audio
> maps it to UAC_EP_CS_ATTR_FILL_MAX, so next_packet_size() always
> returns maxframesize: wMaxPacketSize 192 / 4 bytes = 48 frames per
> 1 ms packet, whatever rate is selected. At 44.1 kHz the device gets
> 48 frames per packet instead of the nominal 44/45 and plays nothing.
> 
> Measurement with plain ALSA (PipeWire not involved): a 4-second
> S16_LE stereo tone played with `aplay -D hw:UP4,0`, hw_ptr sampled
> from /proc/asound/UP4/pcm0p/sub0/status over 2 seconds:
> 
>   rate     hw_ptr advance    wall time for 4 s of audio
>   48000    47991 frames/s    4.01 s
>   44100    48030 frames/s    3.68 s
> 
> /proc/asound/UP4/stream0 while streaming at 44.1 kHz also shows the
> full packet size:
> 
>   Status: Running
>     Interface = 1
>     Altset = 1
>     Packet Size = 192
>     Momentary freq = 44100 Hz (0x2c.199a)
> 
> Listening tests (through PipeWire): 48 kHz is audible, 44.1 kHz is
> silent, reproducible. There are no errors in dmesg; setting the rate
> works (no "cannot set freq" messages).
> 
> This looks like the MOTU MicroBook IIc case (07fd:0004), which already
> clears FILL_MAX in snd_usb_audioformat_attributes_quirk(). Possibly
> related: the disabled Nura entry (0a12:1243) in quirks-table.h says
> "only the 48 kHz sample rate works for the playback interface" and
> sets FILL_MAX as well; that may be the same effect rather than a
> hardware limit. I can't verify this, I don't have that device.
> 
> As 0a12:xxxx IDs are CSR defaults that other products may share (cf.
> commit 5ebf6b1e4596, bugzilla 199905), note that the change below has
> no effect at 48 kHz: with wMaxPacketSize = 192 and 16-bit stereo,
> packsize[0] = packsize[1] = maxframesize = 48 frames, so the packets
> are identical with or without FILL_MAX. A device with the same ID that
> only works at 48 kHz would not be affected; only lower rates change.
> 
> Suggested change (untested on my side so far):
> 
> diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
> --- a/sound/usb/quirks.c
> +++ b/sound/usb/quirks.c
> @@ -2366,6 +2366,14 @@ void snd_usb_audioformat_attributes_quirk(struct
> snd_usb_audio *chip,
>   */
>   fp->attributes &= ~UAC_EP_CS_ATTR_FILL_MAX;
>   break;
> + case USB_ID(0x0a12, 0x1244):  /* Shanling UP4 */
> + /*
> + * MaxPacketsOnly is set, but the device expects nominal-size
> + * packets. Filling 48 frames per packet at 44.1 kHz results
> + * in silence. No effect at 48 kHz, where both sizes match.
> + */
> + fp->attributes &= ~UAC_EP_CS_ATTR_FILL_MAX;
> + break;
>   case USB_ID(0x1224, 0x2a25):  /* Jieli Technology USB PHY 2.0 */
>   /* mic works only when ep packet size is set to wMaxPacketSize */
>   fp->attributes |= UAC_EP_CS_ATTR_FILL_MAX;
> 
> Environment: Ubuntu 26.04, kernel 7.0.0-34-generic, PipeWire 1.6.2.
> Checked tiwai/sound.git for-next at b61a2369085f (2026-10-02): there
> is no entry for 0a12:1244 yet.

If the above change actually works for your device, it's fine to
apply.  Could you submit a proper patch for upstream?


thanks,

Takashi

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

[Vadym S]

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 S <0xsheff@gmail.com>
---
 sound/usb/quirks.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 38d78b834..3fdf03ce9 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -2366,6 +2366,14 @@ void snd_usb_audioformat_attributes_quirk(struct snd_usb_audio *chip,
 		 */
 		fp->attributes &= ~UAC_EP_CS_ATTR_FILL_MAX;
 		break;
+	case USB_ID(0x0a12, 0x1244):  /* Shanling UP4 */
+		/*
+		 * MaxPacketsOnly is set, but the device expects nominal-size
+		 * packets. Filling 48 frames per packet at 44.1 kHz results
+		 * in silence. No effect at 48 kHz, where both sizes match.
+		 */
+		fp->attributes &= ~UAC_EP_CS_ATTR_FILL_MAX;
+		break;
 	case USB_ID(0x1224, 0x2a25):  /* Jieli Technology USB PHY 2.0 */
 		/* mic works only when ep packet size is set to wMaxPacketSize */
 		fp->attributes |= UAC_EP_CS_ATTR_FILL_MAX;
-- 
2.53.0

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

[Vadym Shevchuk]

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>
---
v2: use the full name in From and Signed-off-by
v1: https://lore.kernel.org/all/20261005094433.32960-1-0xsheff@gmail.com/

 sound/usb/quirks.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 38d78b834..3fdf03ce9 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -2366,6 +2366,14 @@ void snd_usb_audioformat_attributes_quirk(struct snd_usb_audio *chip,
 		 */
 		fp->attributes &= ~UAC_EP_CS_ATTR_FILL_MAX;
 		break;
+	case USB_ID(0x0a12, 0x1244):  /* Shanling UP4 */
+		/*
+		 * MaxPacketsOnly is set, but the device expects nominal-size
+		 * packets. Filling 48 frames per packet at 44.1 kHz results
+		 * in silence. No effect at 48 kHz, where both sizes match.
+		 */
+		fp->attributes &= ~UAC_EP_CS_ATTR_FILL_MAX;
+		break;
 	case USB_ID(0x1224, 0x2a25):  /* Jieli Technology USB PHY 2.0 */
 		/* mic works only when ep packet size is set to wMaxPacketSize */
 		fp->attributes |= UAC_EP_CS_ATTR_FILL_MAX;
-- 
2.53.0

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

[Takashi Iwai]

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