2013/11/19 Alan Stern <[email protected]>:
> Please use Reply-To-All so that your message gets sent to the mailing
> list as well as to me.
Sorry for forgetting that :)
>
> On Sat, 16 Nov 2013, yoma sophian wrote:
>
> hi alan:
>
>> My questions are:
>> 1. in usb driver,
>> ehci-sched.c --> itd_complete ->
>>
>> if (unlikely (t & ISO_ERRS)) {
>> ...................... (case A)
>> } else if (likely ((t & EHCI_ISOC_ACTIVE) == 0)) {
>> ........................ (case b)
>> } else {
>> /* URB was too late */ (case c)
>> urb->error_count++;
>> }
>> EXDEV seems come from above comment " /*URB was too late */"
>> >
>> >> if my conclusion is correct, why we said "urb was too late"?
>> >> Does it mean urb too late to send or too late to service?
>> >
>> > The comment means "too late to service".
>>
>> Does that mean
>> 1. iso complete irq happen but
>> 2. scan_isoc is too late to be called, such as delaying 30 ms, etc.
>>
>> if so, the EHCI_ISOC_ACTIVE will be 0 and should not run into this case.
>
> No, it means the URB was submitted too late for the hardware to carry
> out the transfers at their scheduled times.
Could I said that case mean after the urb is actually _was_ scheduled,
the hardware doesn't service it until timeout?
>
>> >> 2. In my case, the urbs are always submitted with URB_ISO_ASAP.
>> >
>> > URBs with ISO_ASAP are never too late to service. That's part of the
>> > reason I suspect the device stopped sending data.
>
> But that was wrong. So it looks like the EHCI hardware is
> malfunctioning.
>
>>
>> BTW, I have one question.
>> 1. for iso in case:
>> even iso in is too late to send, ehci driver still put those delay itd
>> to the period scheduling list.
>
> This never happens with URB_ISO_ASAP. Instead, if an URB is too late
> to be sent, the driver reschedules it for a later time.
>
>> That mean in token will firing on the bus.
>
> No. During the interval between when the URB _should_ have been
> scheduled and when it actually _was_ scheduled, no IN tokens will be
> sent.
>
> However, in your case it looks like the EHCI controller went crazy and
> didn't send any IN tokens even when it should have.
>
> Here's the first place in your log where a problem occurs:
>
> d8a80400 78915228 C Zi:1:003:2 0:8:111:0 10 0:0:100 0:512:100
> d8a80400 78923303 S Zi:1:003:2 -115:8:0 10 -18:0:512 -18:512:512
> d8a80800 78925390 C Zi:1:003:2 0:8:191:0 10 0:0:100 0:512:100
> d8a80800 78927016 S Zi:1:003:2 -115:8:0 10 -18:0:512 -18:512:512
> d8a80400 78941545 C Zi:1:003:2 0:8:319:10 10 -18:0:0 -18:512:0
>
> In the first two lines, URB d8a80400 completes at 78.915 but doesn't
> get resubmitted until 78.923, which is 8 ms later. In the meantime,
> URB d8a80800 was running, and it completes at 78.925.
>
> Because there is only 2 ms remaining in the pipeline when d8a80400 is
> resubmitted, the URB_ISO_ASAP flag causes it to be delayed. Normally
I am not quite understand what does "URB_ISO_ASAP flag causes it to be
delayed" mean.
Does that mean the 2 ms remaining is caused by "URB_ISO_ASAP"?
> it would have been scheduled to start in uframe 271, but instead it was
> scheduled to start in uframe 319, which was 6 ms later (I don't
> understand why this delay was so large; it shouldn't be more than 2
> ms).
Would you please let my know why you think it shouldn't be more than 2ms?
>This means that 6 schedule slots were left empty -- no IN tokens.
>
> On the last line, you can see where d8a80400 completed after the delay.
> This line is full of -18 errors, which means the hardware did not carry
> out the transfers even though they were added to the schedule well in
> advance. In fact, the hardware did not carry out any more transfers
> until almost 3 seconds later!
>
>> if device response data, ehci driver will go into below a) or b)
>
> No. If the host sends an IN token then the driver will go into case a
> or case b. If the host receives valid data from the device, the driver
> will go into case b.
>
>> if device not response, scan_iso will be called by periodically
>> ehci_work timer and clean it.
>
> If the device does not send data, the driver will go into case a.
Why If the device does not send data, the driver will go into case a. ?
in case a, that mean host get any error from the data he recive.
If no data get from device, how host determine the error from?
> The only reason for the periodic timer to fire is if the hardware isn't
> generating interrupts properly. If that happens, the driver will go
> into case c.
>
>> ehci driver will go in c) and -EXDEV will keep not modify.
>>
>> 1. for iso out case:
>> even iso out is too late to send, ehci driver still put those delay
>> itd to the period scheduling list.
>> That mean out token and out data will firing on the bus.
>
> No, OUT works the same way as IN, except that the device never sends
> anything.
>
>> if device response data, ehci driver will go into below a) or b)
>
> The device never sends anything. If the hardware is working correctly,
> the driver will always go into case b.
>
>> since there is no ACK in iso, ehci driver will never go in c)
>
> The driver will go into case c if the hardware isn't working right.
Howabout below race condition happen for accidentlly run into case C.
Actually in there are bulk/iso interleaving happening on my system.
Suppose itds are submitted then ehci_work is triggered by bulk
interrupt and ehci->isoc_count >0.
The race condition may happen if hardware hasn't handled those itds, right?
BTW, why don't we just turn off period schedule in ehci_poll_PSS like below
(since we turn it on directly in ehci_poll_PSS, right)
if (want == 0) { /* Stopped */
if (ehci->periodic_count > 0)
ehci_set_command_bit(ehci, CMD_PSE);
} else { /* Running */
if (ehci->periodic_count == 0) {
/* Turn off the schedule after a while */
- ehci_enable_event(ehci, EHCI_HRTIMER_DISABLE_PERIODIC,
true);
+ ehci_clear_command_bit(ehci, CMD_PSE);
}
}
>
> Have you tried running the same test using a regular PC, rather than an
> embedded system?
Yes, actually it is usermode usbdriver written with libusb.
And we are try to do the cross-check right now.
Appreciate your kind help,
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