Re: [PATCH] ALSA: usb-audio: add Pioneer DJ DDJ-SZ support

[Hanh Kieu <hhkieu@gmail.com>]

Geraldo Nascimento wrote:
> Are you sure is_pioneer_implicit_fb() isn't returning false and you're
> picking up on a generic sync ep instead?
>
> You should double-check that function is returning true or false because
> it will return false when USB_ENDPOINT_USAGE_IMPLICIT_FB isn't
> set on bmAttributes of a Isochronous IN EP.

Good catch, thanks -- I checked against the real device rather than
assuming.

lsusb -v on the DDJ-SZ shows both endpoints (0x01 OUT, 0x82 IN) as
Isochronous / Asynchronous with Usage Type = Data (bmAttributes = 0x05).
is_pioneer_implicit_fb() accepts the capture endpoint's usage being
either USB_ENDPOINT_USAGE_DATA or USB_ENDPOINT_USAGE_IMPLICIT_FB, not
IMPLICIT_FB exclusively, so Data usage does pass that check.

I also traced snd_usb_parse_implicit_fb_quirk()'s dispatch order for
this device to make sure nothing generic intercepts first: no fixed or
capture quirk-table entry matches 08e4:0191, it isn't UAC2
(bInterfaceClass is vendor-spec, not USB_CLASS_AUDIO), and it isn't the
Roland vendor ID. So is_pioneer_implicit_fb() is the function actually
being reached and returning true for this device, not a coincidental
generic fallback.

Happy to add a comment near the quirk-table entry noting the real
bmAttributes value if that would help future readers.

Thanks,
Hanh Kieu