Re: [REGRESSION] ALSA: usb-audio: Behringer USB-MIDI output stalls, since "Use strings in struct usb_dev for manufacturer & co"

[Jan Lentfer <jan.lentfer@web.de>]

> Thanks for the report.
>
> Can this be fixed by applying the same boot quirk for Behringer CM1A
> (something like below)?
>
> Or do we need explicit usb_string() calls instead?  If yes, which one
> (iProduct, iManufacturer) matters?
>
>
> thanks,
>
> Takashi
>
> -- 8< --
> --- a/sound/usb/quirks.c
> +++ b/sound/usb/quirks.c
> @@ -1785,6 +1785,9 @@ int snd_usb_apply_boot_quirk_once(struct usb_device *dev,
>   	case USB_ID(0x07fd, 0x0008): /* MOTU M Series, 1st hardware version */
>   		return snd_usb_motu_m_series_boot_quirk(dev);
>   	case USB_ID(0x1397, 0x1234): /* Behringer CM1A */
> +	case USB_ID(0x1397, 0x1230): /* Behringer K-2 Mk II */
> +	case USB_ID(0x1397, 0x1249): /* Behringer Kobol Expander */
> +	case USB_ID(0x1397, 0x1256): /* Behringer 2-XM */
>   		return snd_usb_cm1a_boot_quirk(dev);
>   	case USB_ID(0x2717, 0xd005): /* Xiaomi audio connector */
>   		snd_usb_xiaomi_boot_quirk(dev);


The CM1A quirk should be sufficient. No usb_string() is needed.

I reproduced the CM1A quirk's request from userspace on 7.2.8 (usbfs
USBDEVFS_CONTROL, no wake-up udev rule active):

1. Power-cycle the K-2 MK II and send notes: the output stalls as before
    (rawmidi Tx 21, avail 4021, 7 bulk-OUT URBs pending).
2. Send a single GET_DESCRIPTOR(DEVICE, 18 bytes)
    (80 06 0100 0000 0012), nothing else. The pending URBs complete
    immediately (Tx 21 -> 96, buffer drained), and all following MIDI
    output works.

A GET_DESCRIPTOR(STRING 2) instead has the same effect (tested
earlier). So it looks like any standard control request after
SET_CONFIGURATION wakes the endpoint, same as on the CM1A.

I have only verified this on the K-2 MK II (1397:1230). The KOBOL
EXPANDER (1397:1249) and 2-XM (1397:1256) run the same firmware
family, have identical descriptors and show the identical stall, so
I'd expect the quirk to cover them as well.

Thanks,
Jan