On Wed, 12 Nov 2014, Felipe Balbi wrote: > > By the way, does the same sort of thing happen after a transfer > > error (such as a CRC mismatch)? Does the xHCI controller change the > > state to EP_STATE_HALTED? Or does it instead go directly to > > There are a few conditions in which XHCI will change EP state to > EP_STATE_HALTED, one of them is a STALL token from the peripheral and > the others would be really error conditions: Babble, CRC error, etc. > > The spec even has a note about it, which I quote: > > " > A Halt condition or USB Transaction error detected on a USB pipe > shall cause a Running Endpoint to transition to the Halted > state. A Reset Endpoint Command shall be used to clear the Halt > condition on the endpoint and transition the endpoint to the > Stopped state. A Stop Endpoint Command received while an > endpoint is in the Halted state shall have no effect and shall > generate a Command Completion Event with the Completion Code set > to Context State Error. > " > > > EP_STATE_STOPPED? You probably want to treat that case and the STALL > > case as similarly as possible. > > There's already code to deal with that, take a look at > xhci_requires_manual_halt_cleanup() and its callers: Then shouldn't the recovery from a STALL be exactly the same as the recovery from any other sort of transfer error? > > Right. In theory you could do it any time up until the completion > > routine returns. Doing it when you process the failed TD seems like a > > good choice -- advance the dequeue pointer and issue the command at the > > same time. > > My concern here is that this will happen when the first usb_submit_urb() > completes. I wonder if moving this to when the following > usb_submit_urb() is about to start would be better ? No, because there may be some other URBs already on the endpoint queue. If no further URBs are submitted then the queue won't get cleaned up. > I think this has a higher probability of being correct. Class driver > might not queue any URB to a particular after the first Stall, so why > would be move the endpoint away from EP_STATE_HALTED prematurely ? In order to handle the queue. Of course, if the queue is empty then there's no harm in leaving the ep in EP_STATE_HALTED until another URB is submitted. By the same reasoning, when the state is changed to EP_STATE_STOPPED, the doorbell should be rung. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
