reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/srini/nvmem.git/commit/?id=17d6f058403d4e3458ec9c7dae607c065cabe089
        git remote add srini-nvmem https://git.kernel.org/pub/scm/linux/kernel/git/srini/nvmem.git
        git fetch --no-tags srini-nvmem for-6.13
        git checkout 17d6f058403d4e3458ec9c7dae607c065cabe089
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs