ALSA: usb-audio: midi2: Restart output URBs on resume

commit f3c57c9 upstream.

USB MIDI 2.0 suspend saves the endpoint running state, clears it and
kills all endpoint URBs. Resume restores the running state, but only
restarts input endpoints.

For a running output endpoint, this leaves the endpoint marked running
with an empty URB queue. Output transfer progress depends on either the
rawmidi trigger path starting the queue or an output completion refilling
it. After suspend there is no completion left, and output data that
remains queued in the raw UMP or legacy rawmidi buffer can stay stalled
until userspace happens to trigger the stream again.

Restore the saved state with atomic accessors, keep input endpoints
restarted as before, and restart output endpoints that were running before
suspend. Clear the saved suspend state after restoring it.

Fixes: ff49d1d ("ALSA: usb-audio: USB MIDI 2.0 UMP support")
Cc: stable@vger.kernel.org
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260504-usb-midi2-output-resume-v1-1-c089cc8ad3c6@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: CassivsGabriellis

sound/usb/midi2.c

@@ -234,7 +234,7 @@ static void kill_midi_urbs(struct snd_usb_midi2_endpoint *ep, bool suspending)
 	if (!ep)
 		return;
 	if (suspending)
-		ep->suspended = ep->running;
+		atomic_set(&ep->suspended, atomic_read(&ep->running));
 	atomic_set(&ep->running, 0);
 	for (i = 0; i < ep->num_urbs; i++) {
 		if (!ep->urbs[i].urb)
@@ -1197,10 +1197,11 @@ void snd_usb_midi_v2_suspend_all(struct snd_usb_audio *chip)
 
 static void resume_midi2_endpoint(struct snd_usb_midi2_endpoint *ep)
 {
-	ep->running = ep->suspended;
-	if (ep->direction == STR_IN)
+	atomic_set(&ep->running, atomic_read(&ep->suspended));
+	atomic_set(&ep->suspended, 0);
+
+	if (ep->direction == STR_IN || atomic_read(&ep->running))
 		submit_io_urbs(ep);
-	/* FIXME: does it all? */
 }
 
 void snd_usb_midi_v2_resume_all(struct snd_usb_audio *chip)