can not unbind pci device, xen kernel

Dear All,

I can not unbind my PCI device.
It is easy an and well know procedure how to unbind a PCI device:
lspci | grep USB
00:1a.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 06)
00:1d.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 06)

lspci -k

00:1a.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 06)
Subsystem: ASUSTeK Computer Inc. Device 8383
Kernel driver in use: ehci_hcd

00:1d.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 06)
Subsystem: ASUSTeK Computer Inc. Device 8383
Kernel driver in use: ehci_hcd

then echo -n “domain:bus:slot:.role” > /sys/bus/pci…

at this point:
echo -n “0000:1a.0” > /sys/bus/pci/drivers/ehci_hcd/unbind

i get an error message:
-bash: echo: write error: No such device

my config:
Linux linux-n0km 2.6.31.14-0.4-xen #1 SMP 2010-10-25 08:45:30 +0200 x86_64 x86_64 x86_64 GNU/Linux

cat /etc/SuSE-release

rpm -qa | grep xen
xen-4.0.1_01-79.2.x86_64
xen-tools-4.0.1_01-79.2.x86_64
kernel-xen-2.6.31.14-0.4.1.x86_64
xen-libs-4.0.1_01-79.2.x86_64
openSUSE 11.2 (x86_64)
VERSION = 11.2

Please help me, any help appreciated.
Regards,
advOPer