> > Logitech has been kind enough to investigate the problem. It seems a > > hardware bug is triggered when the control transfer transactions are sent > > "too fast". Preliminary results show that the hardware misses the second > > transaction in a control transfer when both the SETUP and IN/OUT > > transactions are in the same USB frame. > > So I guess they never bothered to throw this hardware at Linux before, eh?
That's right, and I suppose they now regret it :-) > You might point out to them that the "usbtest" driver, case 10, does > nothing except throw back-to-back control transfers at peripherals ... and > that it's rare for hardware not to be able to withstand that for minutes at > a time. > > (Though I will observe that for folk writing peripheral controller drivers, > that test is annoyingly good at shaking out nasty cases with races between > three components: the host sending packets, the hardware responding to the > different states of control transfers, and the peripheral side software as > it interacts with both of those.) > > > I was wondering if anyone has ever seen such behaviour with other > > devices. It seems the bug is never triggered when using Microsoft > > Windows, so I suspect that Linux uses a faster scheduler. Is there a way > > to hack the USB scheduler to make it split control transfers across USB > > frames ? We would like to test if the hardware bug would then be still > > triggered. > > Almost every Linux host controller driver just sticks the transfers (e.g. > SETUP, IN/DATA, then OUT/STATUS) into a hardware queue and lets the > controller handle the rest ... which as a rule means back-to-back > transfers, all in the same frame. (Though it depends on scheduling.) That's quite weird, because the hardware problem is not triggered when the webcam is plugged into a Windows box. As far as I know, Logitech hasn't changed the way the control transfers are scheduled by Windows. Laurent Pinchart ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
