reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://github.com/jgunthorpe/linux/commit/4cbce969c519aae8c87f0f72fb43e0e1dd590dc6
        git remote add jgunthorpe https://github.com/jgunthorpe/linux
        git fetch --no-tags jgunthorpe pcie_switch_groups
        git checkout 4cbce969c519aae8c87f0f72fb43e0e1dd590dc6
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-14.3.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=csky olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-14.3.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=csky SHELL=/bin/bash drivers/iommu/