There used to be a command "aticonfig --set-powerstate=1", however it does not seem to exist anymore. I get the message:
Since 12.9 I've been able to underclock my GPU which is good, but when it goes into medium and sometimes high when the load piles on. I've been wanting to force the powerstate to low. The reason being battery, not because the clock speeds would save a little but it will stop it getting to the stage where it uses the fans at all which puts massive drains on the battery.
aticonfig: unrecognized option '--set-powerstate=1' aticonfig: parsing the command-line failed.