reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git/commit/?id=a6f0a6f5377fae42a8028f63c89d544c68f24b60
        git remote add mic https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git
        git fetch --no-tags mic next
        git checkout a6f0a6f5377fae42a8028f63c89d544c68f24b60
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs