reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/commit/?id=a086d6de4fdb629b97a02c3b03fcd64d6074e2ba
        git remote add leon-rdma https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git
        git fetch --no-tags leon-rdma dma-split-v1
        git checkout a086d6de4fdb629b97a02c3b03fcd64d6074e2ba
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash drivers/media/platform/samsung/s3c-camif/