[PATCH 7/9] xhci: retry Stop Endpoint on buggy NEC controllers

[Mathias Nyman <mathias.nyman@linux.intel.com>]

From: Michal Pecio <michal.pecio@gmail.com>

Two NEC uPD720200 adapters have been observed to randomly misbehave:
a Stop Endpoint command fails with Context Error, the Output Context
indicates Stopped state, and the endpoint keeps running. Very often,
Set TR Dequeue Pointer is seen to fail next with Context Error too,
in addition to problems from unexpectedly completed cancelled work.

The pathology is common on fast running isoc endpoints like uvcvideo,
but has also been reproduced on a full-speed bulk endpoint of pl2303.
It seems all EPs are affected, with risk proportional to their load.

Reproduction involves receiving any kind of stream and closing it to
make the device driver cancel URBs already queued in advance.

Deal with it by retrying the command like in the Running state.

Signed-off-by: Michal Pecio <michal.pecio@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 drivers/usb/host/xhci-ring.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index b2116501048c..6a29ebd6682d 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1154,6 +1154,15 @@ static void xhci_handle_cmd_stop_ep(struct xhci_hcd *xhci, int slot_id,
 				break;
 			ep->ep_state &= ~EP_STOP_CMD_PENDING;
 			return;
+		case EP_STATE_STOPPED:
+			/*
+			 * NEC uPD720200 sometimes sets this state and fails with
+			 * Context Error while continuing to process TRBs.
+			 * Be conservative and trust EP_CTX_STATE on other chips.
+			 */
+			if (!(xhci->quirks & XHCI_NEC_HOST))
+				break;
+			fallthrough;
 		case EP_STATE_RUNNING:
 			/* Race, HW handled stop ep cmd before ep was running */
 			xhci_dbg(xhci, "Stop ep completion ctx error, ep is running\n");
-- 
2.25.1