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I've a Kontron KTQM87/mITX board (latest BIOS) with some USB 2.0 and some USB 3.0 ports. The machine runs Ubuntu 14.04, I've tried both with 3.13 and 4.4.6 kernels.

In BIOS, I set xHCI mode to "Enabled". I assume this makes USB 3.0 on.

When I connect a USB3/2 device (such as a mass storage), it only appears as a hi-speed device. When I connect a USB3-only device (Intel Realsense), it doesn't appear at all, not even a single line in dmesg.

Here's my lsusb -t

/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/6p, 5000M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/15p, 480M
    |__ Port 1: Dev 2, If 0, Class=Vendor Specific Class, Driver=pl2303, 12M
    |__ Port 3: Dev 3, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
    |__ Port 8: Dev 4, If 0, Class=Vendor Specific Class, Driver=cpc-usb, 12M
    |__ Port 9: Dev 5, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
    |__ Port 9: Dev 5, If 1, Class=Human Interface Device, Driver=usbhid, 1.5

I assume both buses reported there are actually a single bus, but displayed once for hi-speed devices, and once for super-speed devices. I've never seen anything appear under the super-speed bus. All USB3/2 devices appear under Bus 01, which reports max speed 480M, which is hi-speed.

What can I do to make my USB 3 devices work at super-speed?

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The problem showed to be in bad extender cables. We exchanged them for different ones and now the USB 3.0 devices show up as expected.

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