Comment 15 for bug 764195

And alternately, there are .deb packages that install nvidiabl via dkms available from https://github.com/guillaumezin/nvidiabl/downloads . Currently only 4313CTO models have backlight support by default, but it's only a matter of adding PCI IDs and some basic detection stuff. That stuff can be passed when the module is loaded, check the docs for details.