[PATCH v2] usb: dwc3: gadget: check drained isoc ep

[Michael Grzeschik]

To avoid a potential underrun of an currently drained transfer
we add a check for that scenario in the dwc3_gadget_endpoint_trbs_complete
function. In the case of an empty trb ring, we call the stop_transfer
cmd and avoid the underrun to occur.

Signed-off-by: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx>
---
Changes in v2:
- dropped patch "usb: dwc3: gadget: reclaim the whole started list when request was missed"
- fixed patch "usb: dwc3: gadget: check drained isoc ep"
- dropped patch "usb: dwc3: gadget: check the whole started queue for missed requests in complete"
- Link to v1: https://lore.kernel.org/r/20240307-dwc3-gadget-complete-irq-v1-0-4fe9ac0ba2b7@xxxxxxxxxxxxxx
---
 drivers/usb/dwc3/gadget.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 4df2661f66751..3e9c67799259a 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -3582,13 +3582,26 @@ static bool dwc3_gadget_endpoint_trbs_complete(struct dwc3_ep *dep,
 	if (!dep->endpoint.desc)
 		return no_started_trb;
 
-	if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
-		list_empty(&dep->started_list) &&
-		(list_empty(&dep->pending_list) || status == -EXDEV))
-		dwc3_stop_active_transfer(dep, true, true);
-	else if (dwc3_gadget_ep_should_continue(dep))
+	if (usb_endpoint_xfer_isoc(dep->endpoint.desc)) {
+		/* It is possible that the interrupt thread was delayed
+		 * by scheduling in the system, and therefor the HW has
+		 * already run dry. In that case the last trb in the
+		 * queue is already handled by the hw. By checking the
+		 * HWO bit we know to restart the whole transfer. The
+		 * condition to appear is more likely if not every req
+		 * has the IOC bit set and therefor does not trigger the
+		 * interrupt thread frequently.
+		 */
+		struct dwc3_trb *trb = dwc3_ep_prev_trb(dep, dep->trb_enqueue);
+		unsigned int transfer_in_flight = trb->ctrl & DWC3_TRB_CTRL_HWO;
+
+		if ((list_empty(&dep->started_list) || !transfer_in_flight) &&
+		    (list_empty(&dep->pending_list) || status == -EXDEV))
+			dwc3_stop_active_transfer(dep, true, true);
+	} else if (dwc3_gadget_ep_should_continue(dep)) {
 		if (__dwc3_gadget_kick_transfer(dep) == 0)
 			no_started_trb = false;
+	}
 
 out:
 	/*

---
base-commit: 5bab5dc780c9ed0c69fc2f828015532acf4a7848
change-id: 20240307-dwc3-gadget-complete-irq-1a8ffa347fd1

Best regards,
-- 
Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx>