> -----Original Message----- > From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] > Sent: Friday, August 12, 2011 11:47 PM > To: Xu, Andiry > Cc: Sarah Sharp; linux-usb@xxxxxxxxxxxxxxx > Subject: Re: Missed Service Error event handling > > On Fri, 12 Aug 2011, Andiry Xu wrote: > > > Hi Sarah, > > > > I'm debugging a Missed Service Error event related these days. It's > > cause by some buggy HW behavior, which falsely return a overrun event > > following a MSE event, while the ep ring is actually not empty. > > > > Currently xhci driver handles MSE event in the following ways: > > > > 1. When encounter a MSE event, set ep->skip flag, update event ring > > dequeue pointer and return. > > > > 2. When encounter the next event on this ep, the driver will run the > > do-while loop, fetch td from ep's td_list to find the td > corresponding > > to this event. All tds missed are marked as short transfer(-EXDEV). > > > > The do-while loop will end in two ways: > > 1. If the td pointed by the event trb is found; > > 2. If the ep ring's td_list is empty. > > > > If the next event is a overrun event, the driver will never find the > td, > > and it will loop until the td_list is empty. > > > > Unfortunately, the spinlock is dropped when give back a urb in the > > do-while loop. During the spinlock released period, there are urbs > > submitted and tds added to the td_list. This causes disaster, since > the > > td_list will never be empty and the loop never ends, and the system > > hangs. > > > > There is workaround for this, only run the loop if the event points > to a > > valid td, so there is guarantee the loop will end at some point. > > However, this is not acceptable. If there is only several TDs left > > on the ring, and a MSE event occurs and the HW just skip all the TDs. > > There is no valid event following the MSE event, only a > overrun/underrun > > event occurs. In this case driver must process all the tds. This > issue > > is caused by wrong HW behavior, but I don't want an infinite loop and > > system hang in this case. > > > > Do you have any suggestions on MSE event handling? > > Count the number of TDs on the ring when the MSE event occurs. When > skipping, don't skip more than that number. > Thanks, I think this will do. Thanks, Andiry -- 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
