reproduce (this is a W=1 build):
        # https://github.com/avpatel/linux/commit/e3141898f38de6d63cb78f33d1b1e7bfb00d6e29
        git remote add avpatel https://github.com/avpatel/linux.git
        git fetch --no-tags avpatel riscv_iommu_irqbypass_v2
        git checkout e3141898f38de6d63cb78f33d1b1e7bfb00d6e29

        # install um cross compiling tool for clang build
        # apt-get install binutils-um-linux-gnu
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-19 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-19 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um SHELL=/bin/bash drivers/iommu/