On Mon, 18 Jun 2012, Dave Jones wrote: > This bug has been around for a while. > https://bugzilla.redhat.com/show_bug.cgi?id=746914 > > Seems that something changed circa 2.6.33 which prevents uvcvideo from > getting enough bandwidth when plugged into an ehci port (ohci works) > > anyone have suggestions ? Can we move the discussion of the bug from Fedora's bugzilla onto this mailing list? I don't have the email addresses of the principals, apart from Hans. The usbmon trace attached to comment #13 shows three errors. The first, a fairly innocuous mistake, is that the uvcvideo driver submits requests in which the length values in the iso_frame_desc array are too big. It sets the length of each packet to 3060 instead of 2460, which is the correct value for altsetting 11 according to the lsusb output. More seriously, near the end of the usbmon trace we see that the problems start when no interrupts occur during a period of at least 52 ms (!). Obviously this sort of thing shouldn't happen; either IRQs are lost or some other driver has disabled interrupts for far too long. Since the isochronous pipeline set up by uvcvideo has a depth of only 20 ms, this leads to a sizeable dropout. Finally, we have the EFBIG submission errors. They occurred because the delay in interrupt delivery (52 ms) was longer than ehci-hcd's slop amount (20 ms). This led ehci-hcd to think that the new URBs were being scheduled very far in the future rather than in the past, so it rejected them. Now the question is: Why were interrupts not delivered for such a long period? I'm not at all sure how to find out. Alan Stern -- 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
