Description of problem:
scenario 1:
Boot two upstreams
1 upstream bridge + 2 downstream behind it
--
Seabios can not recognize system disk, only recognize the data disks under downstream. see the attached screenshot of seabios.

scenario 2:
Boot two upstreams
1 upstream bridge + 1 downstream behind it
--
Seabios can recognize system disk, and can boot guest successfully. see the attached screenshot of seabios.


Version-Release number of selected component (if applicable):
seabios-1.7.2.2-10.el7.x86_64
qemu-kvm-rhev-1.5.3-37.el7.x86_64
3.10.0-67.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1.boot guest with 4151115-script.sh script.
# sh 4151115-script.sh 
--
# cat 4151115-script.sh 
#!/bin/sh
num=2

cli="$cli /usr/libexec/qemu-kvm -enable-kvm -M q35 -smp 4 -m 3G -usb -device usb-tablet,id=input0 -name RHEL-Server-7.0-64 -drive file=/home/juli/rhel7_64.raw,if=none,id=hd,format=raw,cache=none,werror=stop,rerror=stop -device virtio-scsi-pci,id=scsi0 -device scsi-hd,drive=hd,scsi-id=0,lun=0,id=scsi_image,bootindex=1 -netdev tap,script=/etc/qemu-ifup,id=netdev0 -device virtio-net-pci,netdev=netdev0,id=device-net0 -spice port=5927,disable-ticketing -vga qxl -monitor stdio -drive file=/home/disk/disk0.qcow2,format=qcow2,if=none,id=disk0 -device virtio-scsi-pci,id=disk0 -device scsi-hd,drive=disk0,scsi-id=0,lun=0 -boot menu=on"

for r in $(seq 2)
do

    cli="$cli -device ioh3420,bus=pcie.0,id=root.$r,slot=$r"
    cli="$cli -device x3130-upstream,bus=root.$r,id=upstream$r"
    echo upstream$r

    for k in $(seq $num)
    do
        cli="$cli -device xio3130-downstream,bus=upstream$r,id=downstream$(((r-1)*$num+k)),chassis=$(((r-1)*$num+k-1))"
        cli="$cli -drive file=/home/disk/disk$(((r-1)*$num+k)).qcow2,if=none,id=drive-virtio0-0-$(((r-1)*$num+k)),format=qcow2,cache=none -device virtio-blk-pci,scsi=off,drive=drive-virtio0-0-$(((r-1)*$num+k)),id=virti0-0-$(((r-1)*$num+k)),multifunction=on,bus=downstream$(((r-1)*$num+k))"

    done

done
echo $i
$cli
----------------
# cat 4151115-creat-disk.sh
#! /bin/sh
DIR="/home/disk"
if [-d "$DIR"]; then
    rm -fr $DIR
    mkdir -p $DIR
else
    mkdir -p $DIR
fi

i=0
while ((i<232)); do
    qemu-img create -f qcow2   $DIR/disk$i\.qcow2  100M
    i=$((i+1))
done
------
2.
3.

Actual results:
seabios can not recognize system disk. Please see the attached screenshot of seabios.

Expected results:
seabios can recognize system disk and can boot guest correctly.

Additional info:
this issue is different with bug 1055337. In this bug, the system disk is not under downstream.