Q:

Diagnose brightness control

Brightness control on my laptop does not work, how can I diagnose if it's unsupported, or a bug? And if it is a bug, what do I include in the bug report?
UPDATE
Thank you for all the responses, specially @Guandalino for the bounty. But unfortunately the laptop in question is no longer functional due to an accident involving water. And as such I cannot actively participate and try the out the potential solutions.
Those still interested in this question, please participate in this discussion at Ask Ubuntu Meta.

A:

There is a step-by-step troubleshooting guide on the wiki.

