Re: [PATCH] ALSA: usb-audio: Apply boot quirk for some Behringer models

[Takashi Iwai]

On Tue, 29 Sep 2026 14:19:45 +0200,
Jan Lentfer wrote:
> 
> > Jan reported that a few Behringer devices became broken since the
> > recent optimization to avoid usb_string() call at probe time at the
> > commit b364a0d23cae ("ALSA: usb-audio: Use strings in struct usb_dev
> > for manufacturer & co").  Interestingly, the devices seem requiring
> > the explicit descriptor read at probing time, and the optimization
> > above dropped it.
> > 
> > There is already a boot quirk for another model, Behringer CM1A
> > (1397:1234), that adds a device descriptor read, and this seems
> > working for them, too.  So just apply the same boot quirk to those
> > affected models:
> >   - Behringer K-2 Mk II (1397:1230)
> >   - Behringer Kobol Expander (1397:1249)
> >   - Behringer 2-XM (1397:1256)
> > 
> > Fixes: b364a0d23cae ("ALSA: usb-audio: Use strings in struct usb_dev for manufacturer & co")
> > Reported-and-tested-by: Jan Lentfer<jan.lentfer@xxxxxx>
> > Closes:https://lore.kernel.org/e7087d42-5e74-4d85-b1c5-b11eff235d41@xxxxxx
> > Signed-off-by: Takashi Iwai<tiwai@xxxxxxx>
> > ---
> >   sound/usb/quirks.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
> > index 294c7026b93c..de6a82a42eb7 100644
> > --- a/sound/usb/quirks.c
> > +++ b/sound/usb/quirks.c
> > @@ -1702,7 +1702,10 @@ int snd_usb_apply_boot_quirk_once(struct usb_device *dev,
> >   	switch (id) {
> >   	case USB_ID(0x07fd, 0x0008): /* MOTU M Series, 1st hardware version */
> >   		return snd_usb_motu_m_series_boot_quirk(dev);
> > +	case USB_ID(0x1397, 0x1230): /* Behringer K-2 Mk II */
> >   	case USB_ID(0x1397, 0x1234): /* Behringer CM1A */
> > +	case USB_ID(0x1397, 0x1249): /* Behringer Kobol Expander */
> > +	case USB_ID(0x1397, 0x1256): /* Behringer 2-XM */
> >   		return snd_usb_cm1a_boot_quirk(dev);
> >   	}
> >   
> > -- 
> 
> 
> Hi Takashi,
> 
> thanks a lot for the quick patch!
> 
> One thought on the scope: Behringer sells a large number of synths and
> drum machines that seem to share the same USB-MIDI firmware platform
> (the ones managed by their "SynthTribe" tool). The three models in the
> patch are simply the ones I tested first. Meanwhile I checked another
> one I own, the CAT (1397:1224): it shows exactly the same stall, and a
> single GET_DESCRIPTOR(DEVICE) from userspace fixes it as well. With the
> CM1A that makes five different 1397 products needing the same wake-up,
> so I'd expect more models to be affected and to show up one by one.
> 
> Since the quirk is just one extra GET_DESCRIPTOR(DEVICE) at probe time,
> which should be harmless for any USB device, would it make sense to
> apply it to the whole vendor ID 0x1397 instead of individual product
> IDs?

Makes sense.

> For reference, what I have seen so far (7.2.7/7.2.8, device hot-plugged,
> no wake-up in place):
> 
>   1397:1224  CAT               stalls, fixed by GET_DESCRIPTOR(DEVICE)
>   1397:1230  K-2 MK II         stalls, fixed by GET_DESCRIPTOR(DEVICE)
>   1397:1249  Kobol Expander    stalls
>   1397:1256  2-XM              stalls
>   1397:125f  PRO 800           fine
>   1397:12a7  Grind             fine
>   26a0:0040  Neutron           fine (different vendor ID)
> 
> So it looks like an older firmware generation is affected and newer
> models are not, but that's only a guess from these few devices.
> 
> Either way, a vendor-wide read would not hurt the ones that don't
> need it.
> 
> Also, to be precise about the Tested-by: I verified the fix by issuing
> the same GET_DESCRIPTOR(DEVICE) request from userspace, not with a
> kernel carrying your patch. I'm happy to test the patch itself if you
> want the tag to reflect that.

Let me respin the fix patch.


thanks,

Takashi