Scott Wood writes:

This provides a way to tell the bootwrapper makefile which device tree to
include by default.  The wrapper can still be invoked standalone to wrap
with a different device tree without reconfiguring the kernel, if that is
desired.

...

+config DEVICE_TREE
+	string "Static device tree source file"
+	help
+	  This specifies the device tree source (.dts) file to be
+	  compiled and included when building the bootwrapper.
+	  If a relative filename is given, then it will be relative
+	  to arch/powerpc/boot/dts.
+
+	  This is required when building a cuImage target for an
+	  older U-Boot, which cannot pass a device tree itself.
+	  Such a kernel will not work with a newer U-Boot that
+	  tries to pass a device tree (unless you tell it not to).
+	  If your U-Boot does not mention a device tree in
+	  "help bootm", then use the cuImage target and specify
+	  a device tree here.  Otherwise, use the uImage target.

Hmmm, I'm not sure that I want to be asked about CONFIG_DEVICE_TREE on
*all* powerpc platforms...  Surely this option should depend on
something that says we're including support for a uBoot-able platform?

Paul.