Description of problem:
Boot guest with >=21 xhci controler, seabios will give info "No bootable device".
Then sendkey ctrl-alt-delete to reboot qemu-kvm. But qemu-kvm will hang at booting seabios.


Version-Release number of selected component (if applicable):
seabios-bin-1.7.2.2-10.el7.x86_64
qemu-kvm-1.5.3-41.el7.x86_64
3.10.0-79.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1.Boot guest with >=21 xhci controler via the following shell script.
# sh 4230878-capability-of-xhci-attached-to-switch.sh 21
# cat 4230878-capability-of-xhci-attached-to-switch.sh
#! /bin/sh
CLI="/usr/libexec/qemu-kvm -S -M q35 -m 4G -smp 4,socket=2,core=2,thread=1 \
-device virtio-scsi-pci,bus=pcie.0,id=scsi,addr=0x6 \
-drive file=/home/juli/rhel7.0.qcow2,format=qcow2,if=none,media=disk,id=aa \
-device scsi-hd,drive=aa,id=sys-image,bootindex=0 \
-boot menu=on,strict=on \
-monitor stdio \
-serial unix:/tmp/ttyS0,server,nowait \
-spice port=5931,disable-ticketing \
-vga qxl -global qxl-vga.revision=3 \
-chardev stdio,id=log \
-device isa-debugcon,iobase=0x402,chardev=log"
CLI="$CLI -device ioh3420,bus=pcie.0,id=root.0 "
CLI="$CLI -device x3130-upstream,bus=root.0,id=upstream1,multifunction=on "
CLI="$CLI -device xio3130-downstream,bus=upstream1,id=downstream1,chassis=1 "
NUM_DOWNSTREAM=${1:-255}
for ((i=1,i_downstream=1;i<=$NUM_DOWNSTREAM;i++,i_downstream++)); do
    #m=$((i/7))
    #n=$((i%7+1))
    #m=`printf "%02x" $m`
    #n=`printf "%02x" $n`
#echo $i_downstream
    CLI="$CLI -device nec-usb-xhci,bus=downstream1,id=usb_controller$i"
    CLI="$CLI -drive file=/home/juli/usb-storages/usb$i,if=none,format=qcow2,id=aa-usb$i,media=disk "
    CLI="$CLI -device usb-storage,drive=aa-usb$i,bus=usb_controller$i.0,id=device-usb$i"
done
$CLI

2.sendkey ctrl-alt-delete via HMP when seabios give info "No bootable device".
(qemu) sendkey ctrl-alt-delete
3.

Actual results:
(qemu) sendkey ctrl-alt-delete
(qemu) In resume (status=0)
In 32bit resume
Attempting a hard reboot
xhci: reset while running!
xhci: reset while running!
xhci: reset while running!
xhci: reset while running!
xhci: reset while running!
xhci: reset while running!
xhci: reset while running!
Start bios (version seabios-1.7.2.2-10.el7)
Ram Size=0xb0000000 (0x0000000050000000 high)
Relocating low data from 0x000e4140 to 0x000ef780 (size 2161)
Relocating init from 0x000e49b1 to 0xaffe2e30 (size 53415)

Expected results:
No seabios hang. Can see the seabios info "No bootable device" again.

Additional info: