USB host controller driver
##########################

This driver is capable to serve different controller types, which a platform
offers, like OHCI, UHCI, EHCI, and XHCI.

BIOS Handoff
~~~~~~~~~~~~

Per default the driver performs a hand off of the USB controller from the
BIOS, since it still may access the controller when booting, for example, from
an USB device. The BIOS hand off induces the execution of BIOS/SMM USB driver
code and potentially DMA operations. Unfortunately, some ACPI tables report
wrong RMRR information, which implicates IOMMU faults on illegal DMA
operations and consequently the hand off may fail after noticeably long
timeouts. Therefore, the hand off can be disabled in the USB driver
configuration like follows.

!+ config | bios_handoff: no -
