Should I enabled or disable xHCI hand-off in BIOS setup, when running Windows 7?

I asked over at Intel Communities to try get to the bottom of this. It turns out Intel Engineering has something to say about this:

"According to engineering, it is necessary to leave it as “enabled” for xHCI".

Does the Intel USB 3.0 driver for 7-series chipsets support xHCI hand-off?

So that's that then. When running Windows 7 + Intel's USB 3.0 drivers, xHCI hand-off must be ENABLED in the BIOS setup.

I found an interesting bug relating to EHCI handoff - it may only be on some motherboards.

For later operating systems, you would normally run with EHCI handoff disabled.

On an Asus M4A89GTD Pro/USB3 (and maybe others) if you need to use USB legacy support to allow BIOS control with a USB keyboard, then you must also enable EHCI handoff, otherwise several USB controllers will fail with code 10.

If suffering from this problem, you must uninstall the failed controllers in Device Manager, and then allow them to be redetected - they should then come back OK ... I thought I'd blown some USB ports until I found that.