reproduce:
        git remote add sailus-media-tree git://linuxtv.org/sailus/media_tree.git
        git fetch --no-tags sailus-media-tree metadata
        git checkout 8e5bf1f62e3753a0172060ede618b246677f041e
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs