devicetree: Add minimal support with RPi bootloader

[RPi DT info] https://github.com/raspberrypi/documentation/blob/master/configuration/device-tree.md#part-3-using-device-trees-on-raspberry-pi

RPi bootloader detects a DT-ready kernel by checking for a specific trailer in kernel.img.
Using latest raspberrypi/firmware (firmware.inc) enables this check ability.
Using latest raspberrypi/tools (rpi-mkimage.bb) gives access to mkknlimg for adding the
required trailer to kernel image.


If KERNEL_DEVICETREE is filled in, the trailer is added to the kernel image before
kernel install task. While creating the SDCard image, this modified kernel is
put on boot partition (as kernel.img) as well as DeviceTree blobs (.dtb files).
If KERNEL_DEVICETREE is empty, this new process isn't operated, legacy one does.

KERNEL_DEVICETREE for RPi is really supported only starting from linux-rapsberry 3.18+
kernels, so as for now it defaults to empty (in machine config file).

Change-Id: Ifea71bbda729b8f3c47be7ba0ba03be5ad2ceeaa
Signed-off-by: Francois Muller <francois@concept-embarque.fr>

2 files changed, 29 insertions, 0 deletions

diff --git a/recipes-kernel/linux/linux-raspberrypi.inc b/recipes-kernel/linux/linux-raspberrypi.inc
index 4145b1a..ff0c5ce 100644
--- a/recipes-kernel/linux/linux-raspberrypi.inc
+++ b/recipes-kernel/linux/linux-raspberrypi.inc
@@ -21,6 +21,20 @@ CMDLINE_raspberrypi = "dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA
 
 UDEV_GE_141 ?= "1"
 
+# Set programmatically some variables during recipe parsing
+# 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)
+
+    # Add dependency to 'rpi-mkimage-native' package only if RPi bootloader is used with DT-enable kernel
+    if kerneldt:
+        if kerneltype != 'uImage' and len(kerneldt.strip()) > 1:
+            depends = d.getVar("DEPENDS", True)
+            depends = "%s rpi-mkimage-native" % depends
+            d.setVar("DEPENDS", depends)
+}
+
 do_kernel_configme_prepend() {
     install -m 0644 ${S}/arch/${ARCH}/configs/${KERNEL_DEFCONFIG} ${WORKDIR}/defconfig || die "No default configuration for ${MACHINE} / ${KERNEL_DEFCONFIG} available."
 }
@@ -34,3 +48,13 @@ do_deploy_append() {
     install -d ${DEPLOYDIR}/bcm2835-bootfiles
     echo "${CMDLINE}" > ${DEPLOYDIR}/bcm2835-bootfiles/cmdline.txt
 }
+
+do_rpiboot_mkimage() {
+    if test "x${KERNEL_IMAGETYPE}" != "xuImage" ; then
+        if test -n "${KERNEL_DEVICETREE}"; then
+            # Add RPi bootloader trailer to kernel image to enable DeviceTree support
+            ${STAGING_DIR_NATIVE}/usr/lib/rpi-mkimage/mkknlimg --dtok ${KERNEL_OUTPUT} ${KERNEL_OUTPUT}
+        fi
+    fi
+}
+addtask rpiboot_mkimage before do_install after do_compile
diff --git a/recipes-kernel/linux/linux-raspberrypi_3.18.5.bb b/recipes-kernel/linux/linux-raspberrypi_3.18.5.bb
new file mode 100644
index 0000000..663522e
--- /dev/null
+++ b/recipes-kernel/linux/linux-raspberrypi_3.18.5.bb
@@ -0,0 +1,5 @@
+SRCREV = "a6cf3c99bc89e2c010c2f78fbf9e3ed478ccfd46"
+SRC_URI = "git://github.com/raspberrypi/linux.git;protocol=git;branch=rpi-3.18.y \
+           file://sl030raspberrypii2ckernel.patch \
+          "
+require linux-raspberrypi.inc