[PATCH v3 3/3] usb: xhci: Avoid queuing redundant Stop Endpoint commands

[Michal Pecio <michal.pecio@gmail.com>]

Stop Endpoint command on an already stopped endpoint fails, which may be
misinterpreted as a hardware bug by the completion handler. This results
in an unnecessary delay with repeated retries of the command.

Avoid queuing this command when our endpoint state indicates that it is
pointless: when other endpoint management commands are pending and will
process cancelled TDs on completion, or when the endpoint is waiting for
TT buffer to be cleared.

This should reduce unnecessary retries to almost zero. Known exceptions
include hard endpoint reset not followed by a ring restart and HW faults
causing the endpoint never to restart at all.

The endpoint reset case is likely a bug, so dealing with it is left for
later, when the matter is analyzed and resolved satisfactorily.

Fixes: fd9d55d190c0 ("xhci: retry Stop Endpoint on buggy NEC controllers")
CC: stable@vger.kernel.org
Signed-off-by: Michal Pecio <michal.pecio@gmail.com>
---
 drivers/usb/host/xhci-ring.c | 13 +++++++++++++
 drivers/usb/host/xhci.c      | 24 ++++++++++++++++++++----
 drivers/usb/host/xhci.h      |  1 +
 3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 52eb3ee1d7bf..7726168b72ab 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1071,6 +1071,19 @@ static int xhci_invalidate_cancelled_tds(struct xhci_virt_ep *ep)
 	return 0;
 }
 
+/*
+ * Erase queued TDs from transfer ring(s) and give back those the xHC didn't
+ * stop on. If necessary, queue commands to move the xHC off cancelled TDs it
+ * stopped on. Those will be given back later when the commands complete.
+ *
+ * Call under xhci->lock on a stopped endpoint.
+ */
+void xhci_process_cancelled_tds(struct xhci_virt_ep *ep)
+{
+	xhci_invalidate_cancelled_tds(ep);
+	xhci_giveback_invalidated_tds(ep);
+}
+
 /*
  * Returns the TD the endpoint ring halted on.
  * Only call for non-running rings without streams.
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 1ed4dce7eeb7..e75a6bf4e8d5 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -1680,6 +1680,7 @@ static int xhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 	unsigned long flags;
 	int ret, i;
 	u32 temp;
+	bool cancelled = false;
 	struct xhci_hcd *xhci;
 	struct urb_priv	*urb_priv;
 	struct xhci_td *td;
@@ -1766,13 +1767,28 @@ static int xhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 			td->cancel_status = TD_DIRTY;
 			list_add_tail(&td->cancelled_td_list,
 				      &ep->cancelled_td_list);
+			cancelled = true;
 		}
 	}
 
-	/* Queue a stop endpoint command, but only if this is
-	 * the first cancellation to be handled.
-	 */
-	if (!(ep->ep_state & EP_STOP_CMD_PENDING)) {
+	if (!cancelled)
+		goto done;
+
+	/* These completion handlers will sort out cancelled TDs for us */
+	if (ep->ep_state & (EP_STOP_CMD_PENDING | EP_HALTED | SET_DEQ_PENDING)) {
+		xhci_dbg(xhci, "Not queuing Stop Endpoint on slot %d ep %d in state 0x%x\n",
+				urb->dev->slot_id, ep_index, ep->ep_state);
+		goto done;
+	}
+
+	/* In this case no commands are pending but the endpoint is stopped */
+	if (ep->ep_state & EP_CLEARING_TT) {
+		/* and cancelled TDs can be given back right away */
+		xhci_dbg(xhci, "Invalidating TDs instantly on slot %d ep %d in state 0x%x\n",
+				urb->dev->slot_id, ep_index, ep->ep_state);
+		xhci_process_cancelled_tds(ep);
+	} else {
+		/* Otherwise, queue a new Stop Endpoint command */
 		command = xhci_alloc_command(xhci, false, GFP_ATOMIC);
 		if (!command) {
 			ret = -ENOMEM;
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 0bef6c8b51cf..33e57f408e86 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1914,6 +1914,7 @@ void xhci_ring_doorbell_for_active_rings(struct xhci_hcd *xhci,
 void xhci_cleanup_command_queue(struct xhci_hcd *xhci);
 void inc_deq(struct xhci_hcd *xhci, struct xhci_ring *ring);
 unsigned int count_trbs(u64 addr, u64 len);
+void xhci_process_cancelled_tds(struct xhci_virt_ep *ep);
 
 /* xHCI roothub code */
 void xhci_set_link_state(struct xhci_hcd *xhci, struct xhci_port *port,
-- 
2.43.0