reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # clang-21 might not be officially released. Try a lower version if installation fails.
        # https://github.com/weiny2/linux-kernel/commit/638e1d5342d06b4a65368753d80ffee77d9ea821
        git remote add weiny2 https://github.com/weiny2/linux-kernel.git
        git fetch --no-tags weiny2 dcd-v6-2025-04-13
        git checkout 638e1d5342d06b4a65368753d80ffee77d9ea821
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash drivers/cxl/core/