reproduce (this is a W=1 build):
        # https://github.com/AsahiLinux/linux/commit/679ee8da9f5f0497de57348d1c60a8a856f411b2
        git remote add asahilinux https://github.com/AsahiLinux/linux
        git fetch --no-tags asahilinux bits/020-dart
        git checkout 679ee8da9f5f0497de57348d1c60a8a856f411b2

        # 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/iommu/