I've just checked in a change that allows one to build yaffs2 in one of
two ways:
 
1) In the kernel source tree -- by using the patch-ker.sh script to copy
the yaffs2 source into the kernel tree and modify fs/Kconfig and
fs/Makefile to allow yaffs2 to be included as a file system.
 
In this approach, yaffs2 is configured using kconfig in the usual way.
It is a filesystem in "Miscellaneous filesystems" and you can set the
configuration options there.
 
If you do this, you can build yaffs2 as either a loadable module, or an
in-kernel component.
 
2) Out of the kernel source tree -- this follows the usual module
building process for 2.6 kernels documented in
Documentation/kbuild/modules.txt
 
In this approach, yaffs2 is configured by editing moduleconfig.h and
setting configuration flags appropriately.  You may only build yaffs2 as
a loadable module this way, of course.
 
My apologies to the people who tried this in the past couple of days.  I
made a poor first choice at the variable to use to protect
moduleconfig.h and it was being referenced in both in and out cases.
I've fixed that.
 
Marty