To make the cp2101 driver from this code base:

cp -a cp2103 cp2103.build
cd cp2103.build
./configure
vi cp2101.c
  replace #include "usb-serial.h" with
  #include "/path/to/usb-serial.h"
  The file is found in linux source; may have to download it
make -f Makefile.go all
sudo make -f Makefile.go install
to test: sudo modprobe cp2101, or plug in a device

For newer kernels (2.6.20+):

cp -a cp2103 cp2103.build
cd cp2103.build
./configure -kver `uname -r`
make -f Makefile.go all
chmod a+x installmod
sudo make -f Makefile.go install
to test: sudo modprobe cp2101, or plug in a device