Patch "xhci: always handle "Command Ring Stopped" events" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

xhci: always handle "Command Ring Stopped" events

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xhci-always-handle-command-ring-stopped-events.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mathias Nyman <[email protected]>
Date: Tue, 16 Aug 2016 10:18:03 +0300
Subject: xhci: always handle "Command Ring Stopped" events

From: Mathias Nyman <[email protected]>

commit 33be126510974e2eb9679f1ca9bca4f67ee4c4c7 upstream.

Fix "Command completion event does not match command" errors by always handling the command ring stopped events.

The command ring stopped event is generated as a result of aborting or stopping the command ring with a register write. It is not caused by a command in the command queue, and thus won't have a matching command in the comman list.

Solve it by handling the command ring stopped event before checking for a matching command.

In most command time out cases we abort the command ring, and get a command ring stopped event. The events command pointer will point at the current command ring dequeue, which in most cases matches the timed out command in the command list, and no error messages are seen.

If we instead get a command aborted event before the command ring stopped event, the abort event will increse the command ring dequeue pointer, and the following command ring stopped events command pointer will point at the next, not yet queued command. This case triggered the error message

---
 drivers/usb/host/xhci-ring.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

@@ -1331,12 +1331,6 @@ static void handle_cmd_completion(struct
 
 	cmd = list_entry(xhci->cmd_list.next, struct xhci_command, cmd_list);
 
-	if (cmd->command_trb != xhci->cmd_ring->dequeue) {
-		xhci_err(xhci,
-			 "Command completion event does not match command\n");
-		return;
-	}
-
 	del_timer(&xhci->cmd_timer);
 
 	trace_xhci_cmd_completion(cmd_trb, (struct xhci_generic_trb *) event);

@@ -1348,6 +1342,13 @@ static void handle_cmd_completion(struct
 		xhci_handle_stopped_cmd_ring(xhci, cmd);
 		return;
 	}
+
+	if (cmd->command_trb != xhci->cmd_ring->dequeue) {
+		xhci_err(xhci,
+			 "Command completion event does not match command\n");
+		return;
+	}
+
 	/*
 	 * Host aborted the command ring, check if the current command was
 	 * supposed to be aborted, otherwise continue normally.

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/xhci-don-t-dereference-a-xhci-member-after-removing-xhci.patch queue-4.4/usb-xhci-fix-panic-if-disconnect.patch queue-4.4/usb-define-usb_speed_super_plus-speed-for-superspeedplus-usb3.1-devices.patch queue-4.4/xhci-always-handle-command-ring-stopped-events.patch