reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/lee/leds.git/commit/?id=e14d879292b0f7755c0d51b82a19b30859bb080a
        git remote add lee-leds https://git.kernel.org/pub/scm/linux/kernel/git/lee/leds.git
        git fetch --no-tags lee-leds for-leds-next
        git checkout e14d879292b0f7755c0d51b82a19b30859bb080a
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs