[PATCH v2] Pioneer devices: engage implicit feedback sync for playback

[Olivia Mackintosh]

On Mon, Apr 05, 2021 at 10:49:20AM -0300, Geraldo wrote:
> Dear Linux users of Pioneer gear, please disregard v1 of this patch and
> test this instead if at all possible.
> 
> My initial assessment that we needed to let the capture EP be opened twice
> was clearly proven wrong by further testing. This is good because if we
> really needed that it would require a lot of reengineering inside ALSA.
> 
> One thing that still boggles my mind though is why we need a special
> Pioneer case inside snd_usb_parse_implicit_fb_quirk that returns 1 like a
> capture quirk was found.
> 
> This is a highly experimental patch on top of 5.12-rc6 that's supposed to
> engage implicit feedback sync on the playback for Pioneer devices. Without
> implicit feedback sync the inputs started glitching due to clock drift in
> about an hour in my Pioneer DJ DDJ-SR2.
> 
> Once again I'd like to thank Takashi Iwai. He's the true author of the bulk
> of this code, I just adapted it and coerced it into working.
> 
> Signed-off-by: Geraldo Nascimento <geraldogabriel at gmail.com>

Thank you Geraldo and Takashi for working on this patch. I'm currently
in the process of testing with the DJM-750 but it currently does not
work as expected. I'll debug futher and report back but would like to
make you aware of this in the meantime. It may not be a a fundamental
issue with the patch, but rather something incidental.

Kind regards,
Olivia