[linux-uvc-devel] USB3 vs USB2 bus bandwidth errors

[Patrick White]

I have the following devices:

HP EliteDesk 800 G2 Small Form Factor PC
Magewell USB Capture HDMI ( http://www.magewell.com/usb-capture-hdmi )
Logitech C920


*Scenario 1:*- Running 14.04 with the 4.2 kernel
- If I plug the C920 in USB2 and Magewell in USB3
- Starting either device results in "bus bandwidth" errors.
- Files: 2nd half of dmesg_usb2_then_usb3.txt, lsusb_v_42.txt, and
lsusb3.txt


*Scenario 2:*- Running 14.04 with the 4.2 kernel
- If I plug the C920 in USB2 and Magewell in USB2
- starting either device (or both at the same time) works, but the Magewell
only captures at 8 FPS.
- Files: 1st half of dmesg_usb2_then_usb3.txt, lsusb2.txt


*Scenario 3:*- Running 14.04 with the 3.19 kernel
- If I plug the C920 in USB2 and Magewell in USB3
- starting either device works, with both running at 30 FPs.
- Files: 1st half of dmesg_usb3_319.txt, lsusb3_319.txt

What change between 3.19 and 4.2 kernel could cause behaviour like this?
I'm guessing that the main reason would be some detail like bus bandwidth
errors, and so I tried doing the


*"modprobe uvcvideo quirks=128" *
to run the UVC_QUIRK_FIX_BANDWIDTH but it didn't help at all.
It might be because we capture from C920 with MJPG, but we do use YUYV or
RGB3 for the Magewell and the quirk didn't help.