Great job on the Android 7 image, a lot of things now really work out of the box!
Did some experiments with a magewell usb 3.0 capture card on the usb 3.0 host port of the FireFly rk3399 running the Android 7.1.1 image, and it is automatically recognized as a camera.
[10459.993254] usb 4-1: USB disconnect, device number 6
[15588.049637] usb 4-1: new SuperSpeed USB device number 8 using xhci-hcd
[15588.062517] usb 4-1: LPM exit latency is zeroed, disabling LPM.
[15588.063168] usb 4-1: config 1 has an invalid interface number: 9 but max is 4
[15588.063185] usb 4-1: config 1 has no interface number 4
[15588.064492] usb 4-1: New USB device found, idVendor=2935, idProduct=0006
[15588.064509] usb 4-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[15588.064519] usb 4-1: Product: USB Capture HDMI
[15588.064528] usb 4-1: Manufacturer: Magewell
[15588.064537] usb 4-1: SerialNumber: D206170410576
[15588.070733] uvcvideo: Found UVC 1.10 device USB Capture HDMI (2935:0006)
[15588.081243] input: USB Capture HDMI as /devices/platform/usb@fe900000/fe900000.dwc3/xhci-hcd.10.auto/usb4/4-1/4-1:1.0/input/input14
[15588.133738] hid-generic 0003:2935:0006.0011: hiddev0,hidraw0: USB HID v1.01 Device [Magewell USB Capture HDMI] on usb-xhci-hcd.10.auto-1/input9
However the framerate is not very good, it seems to stall at around 20fps for 1920x1080 YUV2 16bpp (~85mb/s). The card only support grabbing raw formats. The capture card does work to the full 1080p60 on x86 linux hosts (~250mb/s). I’m get 20fps alike performance figures when grabbing the frames directly from the 4vl2 node, so this does seem to be related to the rk3399 usb 3 /drivers.
Is there a limitation in the USB3.0 UVC throughput for the rk3399 or is this a bug/configuration think somewhere in the kernel/sdk ?