Add support for a single kernel config file

chromeos-base/kernel/kernel-0.0.1.ebuild

 # Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=2
 
 inherit toolchain-funcs
 
 DESCRIPTION="Chrome OS Kernel"
 HOMEPAGE="http://src.chromium.org"
 LICENSE="GPL-2"
 SLOT="0"
 KEYWORDS="x86 arm"
 IUSE=""
 
 DEPEND="sys-apps/debianutils"
 RDEPEND=""
 
 kernel=${CHROMEOS_KERNEL:-"kernel/files"}
 files="${CHROMEOS_ROOT}/src/third_party/${kernel}"
 
-if [ "${ARCH}" = "x86" ]; then
-  config=${CHROMEOS_KERNEL_SPLITCONFIG:-"chromeos-intel-menlow"}
-elif [ "${ARCH}" = "arm" ]; then
-  config=${CHROMEOS_KERNEL_SPLITCONFIG:-"qsd8650-st1"}
+# Use a single or split kernel config as specified in the board or variant
+# make.conf overlay. Default to the arch specific split config if an
+# overlay or variant does not set either CHROMEOS_KERNEL_CONFIG or
+# CHROMEOS_KERNEL_SPLITCONFIG. CHROMEOS_KERNEL_CONFIG is set relative 
+# to the root of the kernel source tree.
+
+if [ -n "${CHROMEOS_KERNEL_CONFIG}" ]; then
+        config="${files}/${CHROMEOS_KERNEL_CONFIG}"
+else
+        if [ "${ARCH}" = "x86" ]; then
+                config=${CHROMEOS_KERNEL_SPLITCONFIG:-"chromeos-intel-menlow"}
+        elif [ "${ARCH}" = "arm" ]; then
+                config=${CHROMEOS_KERNEL_SPLITCONFIG:-"qsd8650-st1"}
+        fi
 fi
 
 src_unpack() {
         elog "Using kernel files: ${files}"
 
         mkdir -p "${S}"
         cp -ar "${files}"/* "${S}" || die
 }
 
 src_configure() {
         elog "Using kernel config: ${config}"
-        chromeos/scripts/prepareconfig ${config} || die
+
+        if [ -n "${CHROMEOS_KERNEL_CONFIG}" ]; then
+                cp -f "${config}" "${S}"/.config || die
+        else
+                chromeos/scripts/prepareconfig ${config} || die
+        fi
         emake ARCH=$(tc-arch-kernel) oldconfig || die
 }
 
 src_compile() {
         emake \
           ARCH=$(tc-arch-kernel) \
           CROSS_COMPILE="${CHOST}-" || die
 }
 
 src_install() {
@@ skipping 30 matching lines @@
 
                 cp -a \
                    "${S}"/.config \
                    "${D}/boot/config-${version}" || die
 
                 ln -sf "vmlinuz-${version}"    "${D}"/boot/vmlinuz    || die
                 ln -sf "System.map-${version}" "${D}"/boot/System.map || die
                 ln -sf "config-${version}"     "${D}"/boot/config     || die
         fi
 }