The US-428 pipe-4 output path submits at most one pending p4out
entry from the shared-memory ring per input interrupt. If userspace
queues more than one command before the interrupt handler runs, later
commands remain pending until later input interrupts, even when async
pipe-4 URBs are available.

Drain pending entries while idle async URBs are available. Copy each
command into the existing per-URB async buffer before submission, so the
submitted transfer does not depend on a userspace-mapped ring slot
remaining unchanged after p4out_sent is advanced.

Also update p4out_sent only after usb_submit_urb() succeeds, so a
failed submission is not reported as sent.

This keeps the shared-memory ABI unchanged and fixes only the local
queue-draining behavior.

Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
---
 sound/usb/usx2y/usbusx2y.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/sound/usb/usx2y/usbusx2y.c b/sound/usb/usx2y/usbusx2y.c
index f34e78910200..4190227c5a2a 100644
--- a/sound/usb/usx2y/usbusx2y.c
+++ b/sound/usb/usx2y/usbusx2y.c
@@ -180,7 +180,7 @@ static void i_usx2y_in04_int(struct urb *urb)
 	struct usx2ydev		*usx2y = urb->context;
 	struct us428ctls_sharedmem	*us428ctls = usx2y->us428ctls_sharedmem;
 	struct us428_p4out *p4out;
-	int i, j, n, diff, send;
+	int i, j, n, diff, send, len;
 
 	usx2y->in04_int_calls++;
 
@@ -222,24 +222,31 @@ static void i_usx2y_in04_int(struct urb *urb)
 			} while (!err && usx2y->us04->submitted < usx2y->us04->len);
 		}
 	} else {
-		if (us428ctls && us428ctls->p4out_last >= 0 && us428ctls->p4out_last < N_US428_P4OUT_BUFS) {
-			if (us428ctls->p4out_last != us428ctls->p4out_sent) {
-				send = us428ctls->p4out_sent + 1;
-				if (send >= N_US428_P4OUT_BUFS)
-					send = 0;
-				for (j = 0; j < URBS_ASYNC_SEQ && !err; ++j) {
-					if (!usx2y->as04.urb[j]->status) {
-						p4out = us428ctls->p4out + send;	// FIXME if more than 1 p4out is new, 1 gets lost.
-						usb_fill_bulk_urb(usx2y->as04.urb[j], usx2y->dev,
-								  usb_sndbulkpipe(usx2y->dev, 0x04), &p4out->val.vol,
-								  p4out->type == ELT_LIGHT ? sizeof(struct us428_lights) : 5,
-								  i_usx2y_out04_int, usx2y);
-						err = usb_submit_urb(usx2y->as04.urb[j], GFP_ATOMIC);
+		while (us428ctls &&
+		       us428ctls->p4out_last >= 0 &&
+		       us428ctls->p4out_last < N_US428_P4OUT_BUFS &&
+		       us428ctls->p4out_last != us428ctls->p4out_sent) {
+			for (j = 0; j < URBS_ASYNC_SEQ && !err; ++j) {
+				if (!usx2y->as04.urb[j]->status) {
+					send = us428ctls->p4out_sent + 1;
+					if (send >= N_US428_P4OUT_BUFS)
+						send = 0;
+
+					p4out = us428ctls->p4out + send;
+					len = p4out->type == ELT_LIGHT ?
+						sizeof(struct us428_lights) : 5;
+					memcpy(usx2y->as04.urb[j]->transfer_buffer,
+					       &p4out->val.vol, len);
+					usx2y->as04.urb[j]->transfer_buffer_length = len;
+					err = usb_submit_urb(usx2y->as04.urb[j], GFP_ATOMIC);
+					if (!err)
 						us428ctls->p4out_sent = send;
-						break;
-					}
+
+					break;
 				}
 			}
+			if (j >= URBS_ASYNC_SEQ || err)
+				break;
 		}
 	}
 

---
base-commit: 7c94f5e77906abd7b9ba81875ae238c802a187cb
change-id: 20260428-alsa-usx2y-p4out-drain-9cadb1914706

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

On Tue, 19 May 2026 05:20:41 +0200,
Cássio Gabriel wrote:
> 
> The US-428 pipe-4 output path submits at most one pending p4out
> entry from the shared-memory ring per input interrupt. If userspace
> queues more than one command before the interrupt handler runs, later
> commands remain pending until later input interrupts, even when async
> pipe-4 URBs are available.
> 
> Drain pending entries while idle async URBs are available. Copy each
> command into the existing per-URB async buffer before submission, so the
> submitted transfer does not depend on a userspace-mapped ring slot
> remaining unchanged after p4out_sent is advanced.
> 
> Also update p4out_sent only after usb_submit_urb() succeeds, so a
> failed submission is not reported as sent.
> 
> This keeps the shared-memory ABI unchanged and fixes only the local
> queue-draining behavior.
> 
> Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>

Applied to for-next branch.  Thanks.


Takashi