reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/bristot/linux.git/commit/?id=d8d34b4e3daad9943c806c7cf5273e1594837167
        git remote add bristot git://git.kernel.org/pub/scm/linux/kernel/git/bristot/linux
        git fetch --no-tags bristot sample/dummy_rv
        git checkout d8d34b4e3daad9943c806c7cf5273e1594837167
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs