patch "xhci: always handle "Command Ring Stopped" events" added to usb-linus

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

xhci: always handle "Command Ring Stopped" events

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

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

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(-)

index 918e0c739b79..fe5b70be61ba 100644
@@ -1334,12 +1334,6 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 
 	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);

@@ -1351,6 +1345,13 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 		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.

2.9.3