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

[Takashi Iwai]

On Sun, 18 Apr 2021 16:16:56 +0200,
Geraldo Nascimento wrote:
> 
> Em Dom, 18 de abr de 2021 09:45, Olivia Mackintosh <livvy at base.nu> escreveu:
> 
>     > As a blind shot: might the stall be avoided by passing the recently
>     > introduced chip->playback_first flag?  The revised patch is below.
>    
>     This appears to fix the issue, thank you! I am curious as to why this is
>     not required for Geraldo's DDJ-SR2.
> 
> Heh, sometimes I think Takashi Iwai is psychic ;-)

Heh, it was our luck that we've worked on the similar problem very
recently.

> Just kidding, he's "just" very talented and very experienced. Anyway, the
> DDJ-SR2 is originally a Serato controller. It still requires two MIDI SysEx
> messages to unmute the RCA inputs - engaging "Serato Mode" in marketing-speak.
> 
> My point is that Pioneer may be a little more compliant / a little less
> deviant from the UAC2 standard when designing gear for use with third-party
> software.

I think many devices require the implicit feedback seem following this
pattern: for such devices, the full-duplex streams are mandatory,
i.e. both streams have to be started always.  And the implicit
feedback is triggered at the later point for a proper sync.

>     My initial thought was that certain devices that restrict capture unless
>     regular SysEx/Control URBs are sent may mean that Playback first support
>     is required (e.g. 750, 850, 450). Please correct me if this intuition is
>     incorrect.

As mentioned previously, it might be the difference of the PCM
parameters to be deployed.  I guess Geraldo didn't test speaker-test
program but maybe only the standard sound backends like JACK, etc.

In anyway, I'm going to format and submit the proper patch for
merging.


thanks,

Takashi