1. get kernel and toolchain from github.

git clone https://github.com/raspberrypi/linux.git
git clone https://github.com/raspberrypi/tools.git

1. config kernel source.

   1. generate config.gz from raspberry pi .
      modprobe configs
   2. get config.gz from raspberry pi.
      scp pi@<raspberrypi ip>:/proc/config.gz $HOME/Workspace/raspberrypi/linux
   3. decompress config.gz get .config.
      zcat config.gz > .config
   4. generate kernel config.
      make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- oldconfig

2. compile kernel.
   make ARCH=arm CROSS_COMPIEL=arm-linux-gnueabihf- -j8