This is a BR2_EXTERNAL tree for Buildroot which contains stuff needed to boot a mainline Linux kernel on Samsung's midas (Galaxy S3, Galaxy Note 2) boards.
Clone buildroot:
git clone git://git.buildroot.net/buildroot
Clone this repo:
git clone https://github.com/fourkbomb/buildroot-external-midas
Build it:
make -C buildroot O=$PWD/output BR2_EXTERNAL=$PWD/buildroot-external-midas samsung_midas_defconfig
If you wish to make modifications to the kernel used, clone it somewhere (you probably want to use the master branch)
and edit local.mk.template appropriately:
cp buildroot-external-midas/local.mk.template output/local.mk
vim output/local.mk
Now, start the build in the output directory:
cd output
make
The first build may take a while, so be patient.
To install, you can either use heimdall: heimdall flash --BOOT output/images/boot.img
or use dd on the device: dd if=/path/to/boot.img of=/dev/block/platform/dw_mmc/by-name/BOOT (the path will be different if you're not using the 3.0 vendor kernel).
You can either use a USB-to-UART cable described here, or you can use a plain old USB cable.
Use screen /dev/ttyUSB0 115200 for the USB-to-UART cable, or screen /dev/ttyACM0 for a USB cable.