Under certain situations (typically in the implicit feedback mode),
USB-audio driver starts a playback stream already at PCM prepare call
even before the actual PCM trigger-START call. For implicit feedback
mode, this effectively starts two streams for data and sync
endpoints, and if a coupled sync stream gets XRUN at this point, it
results in an error -EPIPE.
The problem is that currently we return -EPIPE error as is from the
prepare. Then application tries to recover again via the prepare
call, but it'll fail again because the sync-stop is missing. The
sync-stop is missing because it's an internal trigger call (hence the
PCM core isn't involved).
Since we'll need to re-issue the prepare in anyway when trapped into
this pitfall, this patch attempts to address it in a bit different
way; namely, the driver tries to prepare once again after syncing the
stop manually by itself -- so applications don't see the internal
error. At the second failure, we report the error as is, but this
shouldn't happen in normal situations.
Reported-and-tested-by: Carl Hetherington <lists@carlh.net>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/b4e71631-4a94-613-27b2-fb595792630@carlh.net
Link: https://lore.kernel.org/r/20221205132124.11585-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
198dde085e