(In reply to comment #6)
> I tried this on a Fedora Rawhide, I tried to rebuild the provided
> 3.16.0-0.rc4 kernel with the patch. After reboot, I still don't see scaling
> mode in xrandr properties, so no, it doesn't work for me. But maybe I did
> something wrong somewhere, that's very possible.

I suspect you aren't using the patch version of the driver.  You should see the
property.  drm_object_attach_property() is what attaches the property to the
connector.