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

[Geraldo Nascimento]

On Sat, Sep 5, 2026 at 2:35 AM Hanh Kieu <hhkieu@xxxxxxxxx> wrote:
>
> Hi Geraldo,
>
> I looked further into the is_pioneer_implicit_fb() check you pointed out.
>
> It seems the DATA case is intentional. In the original Pioneer DJM-900NXS2 work, Fabian Lesniak described the observed behavior as:
>
> “the playback streams also tries to start the capture endpoint as sync source.”
>
> https://gist.github.com/flesniak/074ab23bbc833663b782f44174eae6a4
>
> Takashi Iwai later formalized this in the Pioneer implicit-feedback handling, explicitly accepting either USB_ENDPOINT_USAGE_DATA or USB_ENDPOINT_USAGE_IMPLICIT_FB for the secondary IN endpoint before passing it to add_implicit_fb_sync_ep():
>
> https://github.com/torvalds/linux/commit/167c9dc84ec384c0940359e067301883ad2b42a8
>

Every other Pioneer device has that USB_ENDPOINT_USAGE_IMPLICIT_FB
on the IN endpoint. Yours would be the first without it in the IN
endpoint. Unless
your hardware doesn't rely on implicit feedback for syncing then there's a good
chance that implicit.c short-circuiting and still picking up implicit
feedback for you
isn't correct, but what you need to do is cool down now and wait for proper
maintainer response which takes time.

Geraldo Nascimento