Comment 7 for bug 1745340

Nova should be explicitly adding USB host controllers, rather than relying on arch specific defaults in this area. That libvirt enabled USB by default on x86 is considered a mistake, so hasn't been copied on other architectures. Even on x86 it is better for Nova to explicitly add USB host controllers, since the default host controller model is USB1 which is a very poor choice.

eg For USB2 the recommended XML would be:

    <controller type='usb' index='0' model='ich9-ehci1'>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <master startport='0'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <master startport='2'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <master startport='4'/>
    </controller>