xhci: fix reporting of 0-sized URBs in control endpoint

When a control transfer has a short data stage, the xHCI controller generates
two transfer events: a COMP_SHORT_TX event that specifies the untransferred
amount, and a COMP_SUCCESS event. But when the data stage is not short, only the
COMP_SUCCESS event occurs. Therefore, xhci-hcd must set urb->actual_length to
urb->transfer_buffer_length while processing the COMP_SUCCESS event, unless
urb->actual_length was set already by a previous COMP_SHORT_TX event.

The driver checks this by seeing whether urb->actual_length == 0, but this alone
is the wrong test, as it is entirely possible for a short transfer to have an
urb->actual_length = 0.

This patch changes the xhci driver to rely on a new td->urb_length_set flag,
which is set to true when a COMP_SHORT_TX event is received and the URB length
updated at that stage.

This fixes a bug which affected the HSO plugin, which relies on URBs with
urb->actual_length == 0 to halt re-submitting the RX URB in the control
endpoint.

Cc: <stable@vger.kernel.org>
Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 11 insertions, 2 deletions

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index b46b5b98a943..5fb66db89e05 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1946,7 +1946,7 @@ static int process_ctrl_td(struct xhci_hcd *xhci, struct xhci_td *td,
         if (event_trb != ep_ring->dequeue) {
                 /* The event was for the status stage */
                 if (event_trb == td->last_trb) {
-                        if (td->urb->actual_length != 0) {
+                        if (td->urb_length_set) {
                                 /* Don't overwrite a previously set error code
                                  */
                                 if ((*status == -EINPROGRESS || *status == 0) &&
@@ -1960,7 +1960,13 @@ static int process_ctrl_td(struct xhci_hcd *xhci, struct xhci_td *td,
                                         td->urb->transfer_buffer_length;
                         }
                 } else {
-                /* Maybe the event was for the data stage? */
+                        /*
+                         * Maybe the event was for the data stage? If so, update
+                         * already the actual_length of the URB and flag it as
+                         * set, so that it is not overwritten in the event for
+                         * the last TRB.
+                         */
+                        td->urb_length_set = true;
                         td->urb->actual_length =
                                 td->urb->transfer_buffer_length -
                                 EVENT_TRB_LEN(le32_to_cpu(event->transfer_len));
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 3b97f0582155..d0663931e5ba 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1,3 +1,4 @@
+
 /*
  * xHCI host controller driver
  *
@@ -1291,6 +1292,8 @@ struct xhci_td {
         struct xhci_segment     *start_seg;
         union xhci_trb          *first_trb;
         union xhci_trb          *last_trb;
+        /* actual_length of the URB has already been set */
+        bool                    urb_length_set;
 };
 
 /* xHCI command default timeout value */