UHCI: Fix handling of short last packet

This patch (as753) fixes the way uhci-hcd handles a short packet when it
is the last packet of an URB.  Right now the driver handles short packets
the same no matter when they occur.  However, the controller stops
transferring packets when the short packet is not the last one (otherwise
it would be reading beyond the end of the device's data) and needs to be
restarted, whereas no such need occurs when the short packet is the last
one.

The result of the bug is that USB endpoint queues experience intermittent
hangs, a regression in 2.6.17 with respect to earlier kernels.  The bug
was raised in Bugzilla #6752 and this patch fixed it.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/host/uhci-q.c b/drivers/usb/host/uhci-q.c
index a06d84c19e13c944f99ffa604cb15034c06ffd42..27909bcf7a1d33c19b181bacdb3c566e57283b86 100644 (file)
--- a/drivers/usb/host/uhci-q.c
+++ b/drivers/usb/host/uhci-q.c
@@ -896,12 +896,14 @@ static int uhci_result_common(struct uhci_hcd *uhci, struct urb *urb)
                        /*
                         * This URB stopped short of its end.  We have to
                         * fix up the toggles of the following URBs on the
-                        * queue and restart the queue.
+                        * queue and restart the queue.  But only if this
+                        * TD isn't the last one in the URB.
                         *
                         * Do this only the first time we encounter the
                         * short URB.
                         */
-                       if (!urbp->short_transfer) {
+                       if (!urbp->short_transfer &&
+                                       &td->list != urbp->td_list.prev) {
                                urbp->short_transfer = 1;
                                urbp->qh->initial_toggle =
                                                uhci_toggle(td_token(td)) ^ 1;