[PATCH] usb: gadget: f_ncm: Restart timer when eth_start_xmit() fails

[Francesco Lavra <flavra@baylibre.com>]

The ncm_tx_timeout() function is run by a timer when unsent data has been
sitting for some time in the NCM driver waiting for more data to be pushed
by the ethernet gadget driver, and calls eth_start_xmit() to trigger a
flush of the unsent data. If there is no available struct usb_request
(which can happen when there is sustained network traffic from the gadget
device to the USB host), the unsent data is not flushed, and remains there
until enough new data has been pushed by the ethernet gadget driver to fill
a USB packet. This can cause outgoing network traffic to stall for several
seconds, during which the gadget device appears unresponsive to the host.

Fix this issue by restarting the ncm_tx_timeout() timer if there is no
available struct usb_request.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 drivers/usb/gadget/function/f_ncm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index 64eabda2f546..fd84086473d7 100644
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -1158,7 +1158,8 @@ static enum hrtimer_restart ncm_tx_timeout(struct hrtimer *data)
 		 *
 		 * This will call directly into u_ether's eth_start_xmit()
 		 */
-		netdev->netdev_ops->ndo_start_xmit(NULL, netdev);
+		if (netdev->netdev_ops->ndo_start_xmit(NULL, netdev) == NETDEV_TX_BUSY)
+			return HRTIMER_RESTART;
 	}
 	return HRTIMER_NORESTART;
 }
-- 
2.39.5