reproduce:
        # https://github.com/Xilinx/linux-xlnx/commit/4622f09ec0ade3749e2465c6a31b2bc7b2c31fad
        git remote add xilinx-xlnx https://github.com/Xilinx/linux-xlnx
        git fetch --no-tags xilinx-xlnx lkp_test
        git checkout 4622f09ec0ade3749e2465c6a31b2bc7b2c31fad
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs