[PATCH] ALSA: usb-audio: midi2: Restart output URBs on resume

[PATCH] ALSA: usb-audio: midi2: Restart output URBs on resume

[Cássio Gabriel]

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: ff49d1df79ae ("ALSA: usb-audio: USB MIDI 2.0 UMP support")
Cc: stable@vger.kernel.org
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
---
 sound/usb/midi2.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/sound/usb/midi2.c b/sound/usb/midi2.c
index 3546ba926cb3..2785600d2312 100644
--- a/sound/usb/midi2.c
+++ b/sound/usb/midi2.c
@@ -227,7 +227,7 @@ 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)
@@ -1188,10 +1188,11 @@ 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)

---
base-commit: fac9a31701803e4e41fdb7b5c71582c65cf47176
change-id: 20260422-usb-midi2-output-resume-3a2867b73ebe

Best regards,
--  
Cássio Gabriel <cassiogabrielcontato@gmail.com>

Re: [PATCH] ALSA: usb-audio: midi2: Restart output URBs on resume

[Takashi Iwai]

On Mon, 04 May 2026 16:08:45 +0200,
Cássio Gabriel wrote:
> 
> 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: ff49d1df79ae ("ALSA: usb-audio: USB MIDI 2.0 UMP support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>

Thanks, applied now.


Takashi