linux-kernel - [PATCH 2/3] usb: dwc3: gadget: check drained isoc ep

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Date: Thu, 07 Mar 2024 16:22:04 +0100
From: Michael Grzeschik <m.grzeschik@...gutronix.de>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Michael Grzeschik <m.grzeschik@...gutronix.de>
Subject: [PATCH 2/3] usb: dwc3: gadget: check drained isoc ep

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@...gutronix.de>
---
 drivers/usb/dwc3/gadget.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index b9fce7b1dcdec..f22b68a0b2dac 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -3568,8 +3568,23 @@ static bool dwc3_gadget_endpoint_trbs_complete(struct dwc3_ep *dep,
 {
 	struct dwc3		*dwc = dep->dwc;
 	bool			no_started_trb = true;
+	unsigned int		transfer_in_flight = 0;
+
+	/* 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.
+	 */
+	if (dep->number && usb_endpoint_xfer_isoc(dep->endpoint.desc)) {
+		struct dwc3_trb *trb = dwc3_ep_prev_trb(dep, dep->trb_enqueue);
+
+		transfer_in_flight = trb->ctrl & DWC3_TRB_CTRL_HWO;
+	}
 
-	if (status == -EXDEV)
+	if (status == -EXDEV || !transfer_in_flight)
 		dwc3_stop_active_transfer(dep, true, true);
 
 	dwc3_gadget_ep_cleanup_completed_requests(dep, event, status);

-- 
2.39.2