[yocto] Building linux-yocto kernel in own bsp layer

[Martin Ertsaas]

Hi.

I'm creating my own bsp layer for omap4 chips (Yes, I know of meta-ti,
but I want to learn how to do this myself :)). I'm trying to use the
linux-yocto 3.4 kernel,
and have gotten it to work locally. I then made a
linux-yocto_3.4.bbappend which contains the following:

COMPATIBLE_MACHINE_pandaboard = "pandaboard"

SRCREV_machine_pandaboard ?= "7eb5fbf903d9db90c3cf371b65e1f2a68d5676d7"

THISDIR := "${@os.path.dirname(bb.data.getVar('FILE', d, True))}"
FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}-3.4"

SRC_URI += "file://defconfig"

do_configure_prepend() {
        cp ${WORKDIR}/defconfig ${S}/.config
}

Problem I get is, without this configure_prepend, my defconfig is not
copied into .config the kernel folder. With this however, I get a
complaint from the kernel that the kernel directory is not clean and I
have to run make mrproper.

I would greatly appreciate any pointer/help/explanations as to what I
have done wrong here, and how to fix it. Have been struggling for this
for a while now, and have no idea what I have done wrong.

Best regards
Martin Ertsaas