Messages in this thread | | | Subject | Re: [PATCH 2/2] usb: host: xhci: Handle the right timeout command | From | Mathias Nyman <> | Date | Mon, 12 Dec 2016 17:52:25 +0200 |
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On 05.12.2016 09:51, Baolin Wang wrote: > If a command event is found on the event ring during an interrupt, > we need to stop the command timer with del_timer(). Since del_timer() > can fail if the timer is running and waiting on the xHCI lock, then > it maybe get the wrong timeout command in xhci_handle_command_timeout() > if host fetched a new command and updated the xhci->current_cmd in > handle_cmd_completion(). For this situation, we need a way to signal > to the command timer that everything is fine and it should exit.
Ah, right, this could actually happen.
> > We should introduce a counter (xhci->current_cmd_pending) for the number > of pending commands. If we need to cancel the command timer and del_timer() > succeeds, we decrement the number of pending commands. If del_timer() fails, > we leave the number of pending commands alone. > > For handling timeout command, in xhci_handle_command_timeout() we will check > the counter after decrementing it, if the counter (xhci->current_cmd_pending) > is 0, which means xhci->current_cmd is the right timeout command. If the > counter (xhci->current_cmd_pending) is greater than 0, which means current > timeout command has been handled by host and host has fetched new command as > xhci->current_cmd, then just return and wait for new current command.
A counter like this could work.
Writing the abort bit can generate either ABORT+STOP, or just STOP event, this seems to cover both.
quick check, case 1: timeout and cmd completion at the same time.
cpu1 cpu2
queue_command(first), p++ (=1) queue_command(more), --completion irq fires-- -- timer times out at same time-- handle_cmd_completion() handle_cmd_timeout(),) lock(xhci_lock ) spin_on(xhci_lock) del_timer() fail, p (=1, nochange) cur_cmd = list_next(), p++ (=2) unlock(xhci_lock) lock(xhci_lock) p-- (=1) if (p > 0), exit OK works
case 2: normal timeout case with ABORT+STOP, no race.
cpu1 cpu2
queue_command(first), p++ (=1) queue_command(more), handle_cmd_timeout() p-- (P=0), don't exit mod_timer(), p++ (P=1) write_abort_bit() handle_cmd_comletion(ABORT) del_timer(), ok, p-- (p = 0) handle_cmd_completion(STOP) del_timer(), fail, (P=0) handle_stopped_cmd_ring() cur_cmd = list_next(), p++ (=1) mod_timer()
OK, works, and same for just STOP case, with the only difference that during handle_cmd_completion(STOP) p is decremented (p--) So unless there is a way to find out if cur_cmd is valid in command timeout in command timeout with the help of existing flags and lists this would be a working solution.
-Mathias
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