Comment # 8 on bug 1120414 from Patrik Jakobsson

Hi Elmar,
According to AMD this would be to run outside of validated specs. Upstream
NACKed it so we cannot accept it either. Sorry.

I understand that it might be tempting to squeeze the most out of your card but
even though it might work for you, someone else could get magic smoke. Also, by
running outside of specs like this, the driver becomes tainted and we cannot
accept bug reports from a tainted driver.

The reason Nouveau have this module parameter is because they are unable to
correctly determine what the _allowed_ clocks actually are. This is not the
case for the Radeon driver. See commit 1a0c96c075bb4 in upstream kernel.