> If output shows ehci, then you are using usb 2, and if output shows xhci,
> then you can use usb 3.
^^^
Can, indeed, but that still depends on other things, such as the actual
setup of the physical port. IIUC most modern Intel chipsets don't come
with EHCI any more and their xHCI handles all the ports, not all of
which are necessarily USB3.
Furthermore, "USB3" is an umbrella term which can refer to various things.
Stefan