fake:

package/base/linux/linux.conf

@@ -100,6 +100,15 @@ fi
 
 auto_config ()
 {
+	case "$arch" in
+		powerpc)
+			defconfig="configs/common_defconfig"
+			;;
+		*)
+			defconfig="defconfig"
+			;;
+	esac
+
 	if [ -f $base/architecture/$arch/kernel$treever.conf.sh ] ; then
 		echo "  using: architecture/$arch/kernel$treever.conf.sh"
 		. $base/architecture/$arch/kernel$treever.conf.sh > .config
@@ -122,11 +131,11 @@ auto_config ()
 		cp $base/architecture/$arch/kernel.conf .config
 	else
 		echo "  using: no rock kernel config found"
-		cp arch/$lx_cpu/defconfig .config
+		cp arch/$lx_cpu/$defconfig .config
 	fi
 
-	echo "  merging (system default): 'arch/$lx_cpu/defconfig'"
-	grep '^CONF.*=y' arch/$lx_cpu/defconfig | cut -f1 -d= | \
+	echo "  merging (system default): 'arch/$lx_cpu/$defconfig'"
+	grep '^CONF.*=y' arch/$lx_cpu/$defconfig | cut -f1 -d= | \
 	while read tag ; do egrep -q "(^| )$tag[= ]" .config || echo "$tag=y"
 	  done >> .config ; cp .config .config.1