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 not only on the urb->actual_length,
but also on the ep_ring->last_td_was_short flag, which is set to true when a
COMP_SHORT_TX event is received.
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 <aleksan...@aleksander.es>
---
Hey,
This is the third update of the patch:
* v2 modified the commit message to make it shorter and clearer.
* v3 updated the format of the commented lines in the patch.
Cheers!
---
drivers/usb/host/xhci-ring.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 88da8d6..eda3276 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1955,7 +1955,7 @@ static int process_ctrl_td(struct xhci_hcd *xhci, struct
xhci_td *td,
/* Did we already see a short data
* stage? */
*status = -EREMOTEIO;
- } else {
+ } else if (!ep_ring->last_td_was_short) {
td->urb->actual_length =
td->urb->transfer_buffer_length;
}
@@ -2447,10 +2447,6 @@ static int handle_tx_event(struct xhci_hcd *xhci,
ret = skip_isoc_td(xhci, td, event, ep, &status);
goto cleanup;
}
- if (trb_comp_code == COMP_SHORT_TX)
- ep_ring->last_td_was_short = true;
- else
- ep_ring->last_td_was_short = false;
if (ep->skip) {
xhci_dbg(xhci, "Found td. Clear skip flag.\n");
@@ -2484,6 +2480,16 @@ static int handle_tx_event(struct xhci_hcd *xhci,
ret = process_bulk_intr_td(xhci, td, event_trb, event,
ep, &status);
+ /*
+ * Flag whether the just processed TRB was short. Do it after
+ * processing, so that the processor methods can also use this
+ * flag.
+ */
+ if (trb_comp_code == COMP_SHORT_TX)
+ ep_ring->last_td_was_short = true;
+ else
+ ep_ring->last_td_was_short = false;
+
cleanup:
/*
* Do not update event ring dequeue pointer if ep->skip is set.
--
2.3.0
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