reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/commit/?id=f71f07bee9b56b94f7828cf3082ea19ec590de36
        git remote add robh https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git
        git fetch --no-tags robh for-next
        git checkout f71f07bee9b56b94f7828cf3082ea19ec590de36
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs