reproduce:
        git remote add android-common https://android.googlesource.com/kernel/common
        git fetch --no-tags android-common android16-6.12
        git checkout 23aadcd1d9764a7dba1c6e3f6d63f89c2ebd435a
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs