reproduce (this is a W=1 build):
        # https://github.com/avpatel/linux/commit/b46a331e996d877983f97d4636e86d9c608bb69b
        git remote add avpatel https://github.com/avpatel/linux.git
        git fetch --no-tags avpatel riscv_acpi_b2_v6_610_rc1_full
        git checkout b46a331e996d877983f97d4636e86d9c608bb69b
        # 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/tty/serial/8250/