Re: Audio interface causing "xhci_hcd ... WARN: buffer overrun event" messages

["Michał Pecio" <michal.pecio@gmail.com>]

Hi,

The 6.12 kernel series is half year old, so this may be unique to your
hardware. Can you try other (ideally similar) UAC devices in the same
USB port, or this device with different xHCI (or EHCI) controllers?

On Wed, 30 Jul 2025 21:02:24 +0100, Bob Ham wrote:
> I'm trying to get an Arturia AudioFuse 16Rig audio interface working
> under Linux.  During loading of snd-usb-audio and when trying to play
> through the interface, the kernel spews a whole bunch of messages
> like so:
> 
> [ 1667.208402] xhci_hcd 0000:00:14.0: WARN: buffer overrun event for
> slot 3 ep 2 on endpoint
> [ 1667.216585] xhci_hcd 0000:00:14.0: WARN: buffer overrun event for
> slot 3 ep 2 on endpoint
> [ 1667.224778] xhci_hcd 0000:00:14.0: WARN: buffer overrun event for
> slot 3 ep 2 on endpoint

"ep 2" means "ep index 2", which is USB endpoint 0x81 aka EP 1 IN.
So this is caused by recording, or maybe by playback while recording,
but not by playback alone.

At face value, "buffer overrun" means that the device sends a packet
which doesn't exceed the endpoint's limit (that would be babble), but
exceeds the data buffer submitted by the UAC driver. In the snippet
above, it seems to be happening regularly every 65 USB microframes.

It could be a UAC issue, or it could still be an xHCI issue if buffer
size is miscommunicated to the hardware or misunderstood by it.

Can you mount debugfs and see if you can find the directory below? It
would tell if there is anything unusual about those 1 in 65 buffers.

/sys/kernel/debug/usb/xhci/0000:00:14.0/


Regards,
Michal