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? 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
