On Thu, 26 Feb 2015, Mathias Nyman wrote: > On 26.02.2015 18:12, Mathias Nyman wrote: > > 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 sets 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 set the urb->actual_length in advance > > to the expected value of a successful control transfer. > > The urb->actual_length is then only adjusted in case of short transfers or > > other special events, but not on COMP_SUCCESS events. > > > > 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: Mathias Nyman <mathias.ny...@linux.intel.com> > > --- > > drivers/usb/host/xhci-ring.c | 73 > > ++++++++++++++++++++++---------------------- > > 1 file changed, 37 insertions(+), 36 deletions(-) > > > > diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c > > index b46b5b9..0e02e79 100644 > > --- a/drivers/usb/host/xhci-ring.c > > +++ b/drivers/usb/host/xhci-ring.c > > @@ -732,7 +732,11 @@ remove_finished_td: > > /* Clean up the cancelled URB */ > > /* Doesn't matter what we pass for status, since the core will > > * just overwrite it (because the URB has been unlinked). > > + * Control urbs have the urb->actual_length pre-set, clear it > > + * as well > > */ > > + if (usb_endpoint_xfer_control(&cur_td->urb->ep->desc)) > > + cur_td->urb->actual_length = 0;
Now this would do the wrong thing if some data had been sent or received before the URB was cancelled. Does the controller write back information about the number of bytes to the data TRB? Maybe it would be easier to get the values from there instead of trying to use the event structures. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
