reproduce:
        git remote add tty https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
        git fetch tty tty-testing
        git checkout tty/tty-testing
        b4 shazam https://lore.kernel.org/r/20240110175221.2335480-4-Frank.Li@nxp.com
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs