[PATCH] ALSA: usb-audio: Apply implicit feedback mode for BOSS devices

[Lucas]

Sorry, in my haste, I mistakenly wrote:

> For me, silence due to the wrong line takes the form of unheard output
> playback, while still working for input capture, so I'm not sure this has
> any bearing on your issue.
>
Output playback silence occurred in one device (Roland INTEGRA-7 on higher
sample rates) which had the line IMPLICIT_FB_FIXED_DEV and needed
IMPLICIT_FB_BOTH_DEV.  So it's the opposite situation.  Capture issues,
such as yours, with arecord were exactly what I saw when a device used
IMPLICIT_FB_BOTH_DEV while needing IMPLICIT_FB_FIXED_DEV instead.

Here's one of my previous examples of a device not compatible with
IMPLICIT_FB_BOTH_DEV:

> Roland VG-99 doesn't capture, but plays well:
> arecord -D hw:VG99 -f S24_3LE -r 44100 -c 2 ./file.wav
> Recording WAVE './file.wav' : Signed 24 bit Little Endian in 3bytes, Rate
> 44100 Hz, Stereo
> arecord: xrun:1672: read/write error, state = PREPARED
>
> aplay -D hw:VG99 -f S24_3LE -r 44100 -c 2 ./other-file.wav
> Playing WAVE './other-file.wav' : Signed 24 bit Little Endian in 3bytes,
> Rate 44100 Hz, Stereo
>

I'm sorry if that caused confusion.  It does seem your issue could be the
very same as the VG-99's above.  That is, a device without "Asynchronous"
"Synch Type" for either of its "IN" or "OUT" endpoints.  In that case,
IMPLICIT_FB_FIXED_DEV should work.

Thanks, and sorry,

  Lucas