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>

1 files changed, 3 insertions, 0 deletions

diff --git a/conf/machine/raspberrypi.conf b/conf/machine/raspberrypi.conf
index 732ba32..01021ca 100644
--- a/conf/machine/raspberrypi.conf
+++ b/conf/machine/raspberrypi.conf
@@ -24,6 +24,9 @@ XSERVER = " \
 
 KERNEL_IMAGETYPE ?= "Image"
 
+# Really supported starting from linux-rapsberry 3.18.y only !
+#KERNEL_DEVICETREE ?= "bcm2708-rpi-b.dtb bcm2708-rpi-b-plus.dtb"
+
 MACHINE_FEATURES = "kernel26 apm usbhost keyboard vfat ext2 screen touchscreen alsa bluetooth wifi sdio"
 
 #RaspberryPi has no hardware clock