> >
> > IMPLICIT_FB_GENERIC_DEV(0x1397, 0x0507),
>
> This should have been enough for ALSA to pick-up the implicit feedback
> mode. Weird...

I tried it once again to confirm. It doesn't work (choppy audio and
"Implicit Feedback Mode: No" as per /proc/asound/card1/stream0).
FYI, this is what I did:

# modprobe -r snd_usb_audio
$ make prepare modules_prepare && make M=sound/usb modules &&\
sudo make M=sound modules_install
# modprobe snd_usb_audio

> BOTH is a quirk for some BOSS devices and at least one Pioneer device,
> don't worry I'm pretty sure your device doesn't need it.
>
> FIXED just means we specify the implicit fb sync ep hardcoded, which
> is obviously a bit bad but it's there because generic matching
> doesn't always work.

Thank you. This confirms my guess. Still no idea why the Scarlett workaround
I saw somewhere uses the capture endpoint in playback_implicit_fb_quirks
(I don't remember the details, but has copied the link; we can look at 
it later
if you are interested).

> Could you please provide the dyndbg of both working and non-working
> cases (without implicit_fb=1)? The documentation for doing so is here
> https://www.kernel.org/doc/html/latest/admin-guide/dynamic-debug-howto.html
>
> Please set snd-usb-audio.dyndbg=+p either at boot time or via debugfs
> before connecting your USB device, then plug it in.

PFA. I'm yet to figure out my way around debugfs, so I copied dmesg. Just
noticed that `Creating new sync endpoint #84` is there when the module 
is loaded
without `implicit_fb=1`. Also, both capture and playback endpoints report
`implicit_fb=0` in the log when the module is loaded without 
`implicit_fb=1`,
while there is a difference when the module is loaded with `implicit_fb=1`.

Thank you,

-- 
Nandakumar Edamana
https://nandakumar.org

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