On Wed, Jun 20, 2012 at 11:23 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 20 Jun 2012, Ming Lei wrote:
>
>> Looks there is an obvious bug in uvcvideo, and the below patch may fix it:
>>
>> diff --git a/drivers/media/video/uvc/uvc_video.c
>> b/drivers/media/video/uvc/uvc_video.c
>> index b76b0ac..d1e7cb2 100644
>> --- a/drivers/media/video/uvc/uvc_video.c
>> +++ b/drivers/media/video/uvc/uvc_video.c
>> @@ -1594,7 +1594,7 @@ static int uvc_init_video(struct uvc_streaming
>> *stream, gfp_t gfp_flags)
>> psize = le16_to_cpu(ep->desc.wMaxPacketSize);
>> psize = (psize & 0x07ff) * (1 + ((psize >> 11) & 3));
>> if (psize >= bandwidth && psize <= best_psize) {
>> - altsetting = i;
>> + altsetting = alts->desc.bAlternateSetting;
>> best_psize = psize;
>> best_ep = ep;
>> }
>
> Yes, that definitely looks like a bug. It could be responsible for the
> wrong packet lengths, although I can't tell from the information in the
> bug report.
>
>> But the bug may not relate with the above.
After further thinking, the patch above may keep MPS consistent with altsetting,
so a correct altsetting should be set into device.
Anyone who has the device may try it.
>>
>> Probably it is caused by mistaken intf->num_altsetting of 12, instead of
>> 13.
>
> How do you know intf->num_altsetting was set to 12?
Just a guess and reasoning, :-)
Because 3060 in iso_frame_desc is corresponding to the last altsetting,
which is set as 11 into the uvc video interface, so I guess intf->num_altsetting
might be set as 12 mistakenly and the problem is triggered.
>
>> Also from the usbmon trace, all packets are completed with length of 12,
>> which indicates that there aren't capture data at all.
>
> Maybe there wasn't supposed to be any. Anyway, that's a separate
> problem.
It might be a result of mismatch between packet size and altsetting set
into device.
>
>> > Now the question is: Why were interrupts not delivered for such a long
>> > period? I'm not at all sure how to find out.
>>
>> Maybe the irqsoff tracer can help troubleshoot it.
>
> What is the irqsoff tracer?
Please see the section of "The Tracers" in Documentation/trace/ftrace.txt.
Also considered that io_watchdog is disabled in intel ehci controller, is it
possible there are no interrupts coming from ehci hardware?
Thanks,
--
Ming Lei
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