reproduce:
        git checkout 0bb71d301869446810a0b13d3da290bd455d7c78
        b4 shazam https://lore.kernel.org/r/20250613-mip4-touchkey-v2-1-9bbbe14c016d@disroot.org
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 3.4.3
        make htmldocs