reproduce (this is a W=1 build):
        # https://github.com/frank-w/BPI-R2-4.14/commit/8616912a95a6ddcfb98477c5c1d7efbf4ba3ab18
        git remote add frank-w-bpi-r2-4.14 https://github.com/frank-w/BPI-R2-4.14
        git fetch --no-tags frank-w-bpi-r2-4.14 6.12-rsslro
        git checkout 8616912a95a6ddcfb98477c5c1d7efbf4ba3ab18
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/spi/