On Wed, Jan 01, 2020 at 08:35:59PM +0200, Laurent Pinchart wrote: > Hi Roger, > > (CCin'g Alan Stern and linux-usb) > > On Wed, Jan 01, 2020 at 05:52:27PM +0000, Roger Whittaker wrote: > > On Wed, Jan 01, 2020 at 07:24:49PM +0200, Laurent Pinchart wrote: > > > > > The last message is worse. Could you send me the output of lsusb -v (you > > > can restrict it to the camera with -d), if possible running as root, for > > > both the working and non-working kernels ? > > > > Thanks very much for your reply. > > > > The lsusb outputs are attached - they are in fact identical to each > > other. > > > > Also attached, the dmesg lines when replugging the camera on both > > kernels. > > Thank you for the information. > > I had missed the following message: > > [ 470.351700] usb 1-1.4.3.1: config 1 interface 2 altsetting 0 endpoint 0x82 has wMaxPacketSize 0, skipping > > This seems to be the culprit, and it points to the USB core. One > interface is ignored due to its wMaxPacketSize value, and the uvcvideo > driver then fails to find it. > > The wMaxPacketSize check was added in > > commit d482c7bb0541d19dea8bff437a9f3c5563b5b2d2 > Author: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > Date: Mon Oct 28 10:52:35 2019 -0400 > > USB: Skip endpoints with 0 maxpacket length > > Endpoints with a maxpacket length of 0 are probably useless. They > can't transfer any data, and it's not at all unlikely that an HCD will > crash or hang when trying to handle an URB for such an endpoint. > > Currently the USB core does not check for endpoints having a maxpacket > value of 0. This patch adds a check, printing a warning and skipping > over any endpoints it catches. > > Now, the USB spec does not rule out endpoints having maxpacket = 0. > But since they wouldn't have any practical use, there doesn't seem to > be any good reason for us to accept them. > > Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > > Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910281050420.1485-100000@xxxxxxxxxxxxxxxxxxxx > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > The commit was merged in v5.4 and backported to v5.3.11 in > 47aaab6377204cdbcd16f52a23c584f994fd0d15. > > For reference for Alan and linux-usb, the issue being discussed is > described in https://bugzilla.suse.com/show_bug.cgi?id=1159811. The > above commit seems to cause a regression with several cameras. I've > attached to this e-mail the lsusb output provided by Roger. How can a device work with an endpoint of 0 length? What does the driver expect to do with those endpoints? Does it expect it to be present but just ignore it? thanks, greg k-h
