[PATCH 3.12 117/175] xhci: fix reporting of 0-sized URBs in control endpoint

[Jiri Slaby]

From: Aleksander Morgado <aleksander@xxxxxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 45ba2154d12fc43b70312198ec47085f10be801a upstream.

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.

Signed-off-by: Aleksander Morgado <aleksander@xxxxxxxxxxxxx>
Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 drivers/usb/host/xhci-ring.c | 10 ++++++++--
 drivers/usb/host/xhci.h      |  3 +++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 6f052daed694..6bf308798a2d 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2100,7 +2100,7 @@ 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) &&
@@ -2114,7 +2114,13 @@ 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 43f0b2ef7b60..d14b3e17b906 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1,3 +1,4 @@
+
 /*
  * xHCI host controller driver
  *
@@ -1284,6 +1285,8 @@ 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 */
-- 
2.3.0

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