[yocto] Specifying location of DTB file

[Adam Rossi]

Howdy folks. I have had a devil of a time creating my own machine.conf
and getting it to boot, so I went back to using the stock
beaglebone.conf machine. I need to modify the DTB file that my
prototype loads, so I decompiled the yocto am335x-boneblack.dtb, added
some special sauce to the dts, and added the following to a
linux-yocto_3.19.bbappend recipe:

FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
SRC_URI +="file://touchscreen.cfg \
 file://special-am335x-boneblack.dts"

do_install_prepend() {
        cp ${WORKDIR}/special-am335x-boneblack.dts ${S}/arch/${ARCH}/boot/dts/
}
KERNEL_DEVICETREE_beaglebone =  "special-am335x-boneblack.dtb"

This works, I get a special-am335x-boneblack.dtb in my image. However,
on booting the files on my beagle bone, I get an error that the system
cannot find the boot/am335x-boneblack.dtb file. Creating a symlink to
my special-am335x-boneblack.dtb solves the problem.

Where does the system configure the directions to look for
"am335x-boneblack.dtb"? I suspect this is because the stock
beaglebone.conf file also has a
KERNEL_DEVICETREE="am335x-boneblack.dtb". Perhaps my kernel recipe is
only partly overriding this?

Thanks for your continuing help. Regards, Adam