Hi Steve, (CC'ing the linux-uvc-devel mailing list, as the information you wrote can be helpful for many people).
On Thursday 10 December 2009 16:21:21 saze...@aol.com wrote: > Laurent, > > Thanks for the reply. I sent the output of dmesg to Paulo and he observed > the camera was connected via a hub. Paulo suspected that the problem may > be caused by a defect in the way that Linux handles hubs. It turns out > that all of the USB ports on my laptop go through a hub. I switched to a > desktop and it worked! > I am using Puppy Linux and I relayed the problem to the Puppy forum. > One of the members off this advice on changing the uvcvideo driver to get > around the hub problem: > > While compiling the 2.6.31.6 kernel, I noticedthis: in order to get true > usb2 speed through my (Intel ICH7) usbports, I must compile the usb2 > driver ehci_hcd into the kernel, not asa module. Otherwise the usb1 driver > (uhci_hcd) grabs the hub'sinterrupts first and doesn't relinquish them to > ehci_hcd. Result:slooooww usb-port operation. I would speculate, too slow > for a webcam. > > I would therefore suggest to the writers of Linux usb webcamdrivers that, > in order to obtain a meaningful probe for a usb2 hub, thewebcam driver > loader should look first at the output of lspci -k,before looking at > lsmod. If the webcam driver loader looks only atlsmod, it will miss the > case where the 2.6.31.6 (and, presumably, allearlier) kernel(s) > is/are/were compiled correctly for usb2 (i.e., withehci_hcd compiled > directly into the kernel, and uhci_hcd and ohci_hcdas modules). > > If the kernel.org team ever makes the kernel do its ehci_hcd probebefore > its uhci_hcd probe, then a mere lsmod probe will suffice. Untilthat happy > day, I would venture to predict there will be muchfrustration in webcam > Linuxland, except among those who are savvyenough to add the necessary > lspci -k probing logic to the webcam driverloader ourselves > > If your camera's driver loader *is* already written to look first atlspci > -k, then all you need in order for the webcam to work is torecompile the > kernel with ehci_hcd compiled directly into the kernel,the other two as > modules. Wuh-laww, now your ICH7 usb2 hub runs at itsintended speed and > your usb webcam (knock on wood) works. > > Don't get carried away and compile usbhid into the kernel as well,though. > It works OK, but it confuses the Puppy shutdown script. > > > Not sure how difficult it is to use lspci -k before lsmod but it might be > worth trying so that users with only hub terminated USB ports can use > uvcvideo. Thanks a lot for the information. You forgot the "lsusb -v -d 046d:0804" output though ;-) -- Regards, Laurent Pinchart _______________________________________________ Linux-uvc-devel mailing list Linux-uvc-devel@lists.berlios.de https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
