reproduce (this is a W=1 build):
        # https://github.com/avpatel/linux/commit/6cf4d904859b744e410d58c0ca3ffe6e56d37b6c
        git remote add avpatel https://github.com/avpatel/linux.git
        git fetch --no-tags avpatel riscv_acpi_b2_v6_610_rc1_full
        git checkout 6cf4d904859b744e410d58c0ca3ffe6e56d37b6c
        # 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/