reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git/commit/?id=ac9888639e961ae0a4bceac5a00698724ae1a940
        git remote add soc https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git
        git fetch --no-tags soc board-remove
        git checkout ac9888639e961ae0a4bceac5a00698724ae1a940
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs