reproduce:
        git checkout fec50db7033ea478773b159e0e2efb135270e3b7
        b4 shazam https://lore.kernel.org/r/20240408-rtc_dtschema-v1-2-c447542fc362@gmail.com
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs