kernel fixes

index a2ec4ca..3913f41 100644
@@ -179,7 +179,8 @@ kernels.
           While creating the SDCard image, this modified kernel is put on
           boot partition (as kernel.img) as well as DeviceTree blobs (.dtb files).
 
-NOTE: KERNEL_DEVICETREE is empty by default.
+NOTE: KERNEL_DEVICETREE is default enabled for kernel >= 3.18 and always disabled for
+      older kernel versions.
 
 3. Extra apps
 =============

new file mode 100644
index 0000000..40beef1
@@ -0,0 +1,39 @@
+inherit linux-kernel-base
+
+
+def get_dts(d, ver):
+    staging_dir = d.getVar("STAGING_KERNEL_BUILDDIR", True)
+    dts = d.getVar("KERNEL_DEVICETREE", True)
+
+    # d.getVar() might return 'None' as a normal string
+    # leading to 'is None' check isn't enough.
+    # TODO: Investigate if this is a bug in bitbake
+    if ver is None or ver == "None":
+        ''' if 'ver' isn't set try to grab the kernel version
+        from the kernel staging '''
+        ver = get_kernelversion_file(staging_dir)
+
+    if ver is not None:
+        min_ver = ver.split('.', 3)
+    else:
+        return dts
+
+    # Always turn off device tree support for kernel's < 3.18
+    try:
+        if int(min_ver[0]) <= 3:
+            if int(min_ver[1]) < 18:
+                dts = ""
+    except IndexError:
+        min_ver = None
+
+    return dts
+
+
+def split_overlays(d, out):
+    dts = get_dts(d, None)
+    if out:
+        overlays = oe.utils.str_filter_out('\S+\-overlay\.dtb$', dts, d)
+    else:
+        overlays = oe.utils.str_filter('\S+\-overlay\.dtb$', dts, d)
+
+    return overlays

index 1ff664d..7592cc1 100644
@@ -1,4 +1,5 @@
 inherit image_types
+inherit linux-raspberrypi-base
 
 #
 # Create an image that can by written onto a SD card using dd.

@@ -70,11 +71,6 @@ SDIMG = "${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.rpi-sdimg"
 # Additional files and/or directories to be copied into the vfat partition from the IMAGE_ROOTFS.
 FATPAYLOAD ?= ""
 
-# Device Tree Overlays are assumed to be suffixed by '-overlay.dtb' string and will be put in a dedicated folder
-DT_ALL = "${@d.getVar('KERNEL_DEVICETREE', True) or ''}"
-DT_OVERLAYS = "${@oe.utils.str_filter('\S+\-overlay\.dtb$', '${DT_ALL}', d)}"
-DT_ROOT = "${@oe.utils.str_filter_out('\S+\-overlay\.dtb$', '${DT_ALL}', d)}"
-
 IMAGEDATESTAMP = "${@time.strftime('%Y.%m.%d',time.gmtime())}"
 
 IMAGE_CMD_rpi-sdimg () {

@@ -90,6 +86,9 @@ IMAGE_CMD_rpi-sdimg () {
 
 	echo "Creating filesystem with Boot partition ${BOOT_SPACE_ALIGNED} KiB and RootFS ${ROOTFS_SIZE_ALIGNED} KiB"
 
+	# Check if we are building with device tree support
+	DTS="${@get_dts(d, None)}"
+
 	# Initialize sdcard image file
 	dd if=/dev/zero of=${SDIMG} bs=1024 count=0 seek=${SDIMG_SIZE}
 

@@ -112,7 +111,11 @@ IMAGE_CMD_rpi-sdimg () {
 		mcopy -i ${WORKDIR}/boot.img -s ${DEPLOY_DIR_IMAGE}/${KERNEL_IMAGETYPE}${KERNEL_INITRAMFS}-${MACHINE}.bin ::uImage
 		;;
 	*)
-		if test -n "${KERNEL_DEVICETREE}"; then
+		if test -n "${DTS}"; then
+			# Device Tree Overlays are assumed to be suffixed by '-overlay.dtb' string and will be put in a dedicated folder
+			DT_OVERLAYS="${@split_overlays(d, 0)}"
+			DT_ROOT="${@split_overlays(d, 1)}"
+
 			# Copy board device trees to root folder
 			for DTB in ${DT_ROOT}; do
 				DTB_BASE_NAME=`basename ${DTB} .dtb`

index 84d4f9e..7e36408 100644
@@ -1,4 +1,5 @@
 require linux.inc
+inherit linux-raspberrypi-base
 
 DESCRIPTION = "Linux Kernel for Raspberry Pi"
 SECTION = "kernel"

@@ -26,7 +27,8 @@ UDEV_GE_141 ?= "1"
 # See http://www.yoctoproject.org/docs/current/bitbake-user-manual/bitbake-user-manual.html#anonymous-python-functions
 python __anonymous () {
     kerneltype = d.getVar('KERNEL_IMAGETYPE', True)
-    kerneldt = d.getVar('KERNEL_DEVICETREE', True)
+    kerneldt = get_dts(d, d.getVar('LINUX_VERSION', True))
+    d.setVar("KERNEL_DEVICETREE", kerneldt)
 
     # Add dependency to 'rpi-mkimage-native' package only if RPi bootloader is used with DT-enable kernel
     if kerneldt: