[PATCH] ALSA: usb-audio: Split endpoint setups for hw_params and prepare (take#2)

[Geoffrey D. Bennett]

Hi Takashi,

On Tue, Sep 20, 2022 at 08:11:06PM +0200, Takashi Iwai wrote:
> This is a second attempt to fix the bug appearing on Android with the
> recent kernel; the first try was ff878b408a03 and reverted at commit
> 79764ec772bc.

I found that full-duplex audio for Scarlett devices was broken in
5.19.11 but working again 5.19.12, presumably due to this. escuta at
https://linuxmusicians.com/viewtopic.php?p=148734#p148734 reported
that it was broken from 5.19.9 but 5.19.8 worked (they also reported
that 5.9.12 didn't work, which I can't explain).

5.19.12 and 6.0.0 work for me, but 6.0.0 + your v2 patch makes the
gnome sound settings app crash when setting the output device to
Scarlett if the input device was already set to Scarlett.

Using the gnome-control-center (42.3) app (Fedora 36, PipeWire 0.3.59,
WirePlumber 0.4.11) to test:

- Kernel 5.19.11: can't set both input and output device to Scarlett;
  changing output to Scarlett makes the input device switch to
  something else, and changing the input device to Scarlett makes the
  output device switch to something else

- Kernel 5.9.12 & 6.0.0: can set both input and output device to
  Scarlett, all good/normal

- Kernel 6.0.0+v2 patch: if both input and output device are already
  set to Scarlett, works fine. Change output device to something else
  then back to Scarlett, the settings app hangs. Kill the app, restart
  it, the input & output device are both Scarlett & it appears to work
  fine again until you change the output device to Scarlett when the
  input device is already Scarlett. Changing it in the other order
  (set input device to Scarlett when output device is already
  Scarlett) works no problem.

Regards,
Geoffrey.