commit e144bb7af49ca8756b7222a75811f3b85b0bc1f5 Author: Gerd Hoffmann email@example.com Date: Mon Jun 3 16:30:18 2013 +0200
usb: add xhci support $subject says all. Support for usb3 streams is not implemented yet, otherwise it is fully functional. Tested all usb devices supported by qemu (keyboard, storage, usb hubs), except for usb attached scsi in usb3 mode (which needs streams). Tested on qemu only, tagged with QEMU_HARDWARE because of that. Testing with physical hardware to be done.
That commit made seabios size (default qemu config, gcc 4.7+) jump from 128k to 256k in size because the code didn't fit into 128k any more.
Most likely the failure isn't related to xhci at all, but to the size change.
You can try to turn off some features (hardware support) you don't need to make the bios image smaller. 1.7.4 also has a config option to explicitly set the image size you want.
IIRC xen combines seabios and hvmloader into a single 256k image somehow, so it might make sense to set the seabios image size to something between 128k and 256k. But better ask the xen people for details here.