reproduce (this is a W=1 build):
        # https://github.com/morimoto/linux/commit/5f5046abae4620e2209def6367c4917313dce94d
        git remote add morimoto https://github.com/morimoto/linux
        git fetch --no-tags morimoto renesas-lts/v6.18-rc5-2025-11-12-sparrow-hawk
        git checkout 5f5046abae4620e2209def6367c4917313dce94d

        # install powerpc64 cross compiling tool for clang build
        # apt-get install binutils-powerpc64-linux-gnu
        # clang-22 might not be officially released. Try a lower version if installation fails.
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # apt-get install sparse
        # sparse version: v0.6.4-71-g610d841d

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=powerpc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=powerpc SHELL=/bin/bash drivers/media/platform/renesas/rcar-isp/