[CentOS] missing from Centos51 src tree: ".../drivers/infiniband/hw/amso1100/Makefile"

i'm attempting to rebuild centos51 kernel-xen.

(fwiw, because pciback has NOT been compiled into the kernel,
	http://bugs.centos.org/view.php?id=2767)

after,

	yum install kernel-devel kernel-xen-devel

and usual,

	ln -s /usr/src/kernels/`uname -r`-`uname -m` /usr/src/linux
	cd /usr/src/linux
	cp /boot/config-`uname -r` ./.config
	make oldconfig
	make menuconfig
	...

next,

	make rpm

fails at,

	scripts/kconfig/conf -s arch/x86_64/Kconfig
	make clean
	scripts/Makefile.clean:17:
/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/amso1100/Makefile:
No such file or directory
	make[5]: *** No rule to make target
`/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/amso1100/Makefile'.
 Stop.
	make[4]: *** [drivers/infiniband/hw/amso1100] Error 2
	make[3]: *** [drivers/infiniband] Error 2
	make[2]: *** [_clean_drivers] Error 2
	make[1]: *** [rpm] Error 2
	make: *** [rpm] Error 2

checking,

	ls -al \
	/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/amso1100/Makefile
\
	/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/*/Makefile
	
in fact *is* missing,

	/bin/ls: /usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/amso1100/Makefile:
No such file or directory
	-rw-r--r-- 1 root root 380 May  7 06:12
/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/cxgb3/Makefile
	-rw-r--r-- 1 root root 545 May  7 06:12
/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/ehca/Makefile
	-rw-r--r-- 1 root root 782 May  7 06:12
/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/ipath/Makefile
	-rw-r--r-- 1 root root 310 May  7 06:12
/usr/src/kernels/2.6.18-53.1.19.el5-xen-x86_64/drivers/infiniband/hw/mthca/Makefile


installing & checking original/full SRPM,

	cd /usr/src/redhat/SRPMS
	wget http://mirror.centos.org/centos/5.1/updates/SRPMS/kernel-2.6.18-53.1.19.el5.src.rpm
	rpm -ivh kernel-2.6.18-53.1.19.el5.src.rpm

it's also missing there,

	ls -al /usr/src/kernels/2.6.18-53.1.19.el5-x86_64/drivers/infiniband/hw/amso1100/Makefile
	/bin/ls: /usr/src/kernels/2.6.18-53.1.19.el5-x86_64/drivers/infiniband/hw/amso1100/Makefile:
No such file or directory

where can I get the 'Makefile'?

thanks.