reproduce:
        git checkout c612261bedd6bbab7109f798715e449c9d20ff2f
        b4 shazam https://lore.kernel.org/r/20260322-mailbox-v1-1-c6251f18187c@gmail.com
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs