reproduce:
        git checkout linux/master
        b4 shazam https://lore.kernel.org/r/20231111024835.2164816-14-tj@kernel.org
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs