My laptop comes with ATI/AMD Mobility Radeon HD 5850 (Evergreen JUNIPER). My system is Debian stretch/testing with 4.2.0-1-amd64 kernel. It is awesome and I don't want to change it, but it is too noisy because overheating of the graphic card. Overheating doesn't depends on the CPU usage.
Xorg (installed version 7.7+12) must support dpm on my graphic card. But probably it isn't works.
P.S. That definetely is not dust or fan problem. Because I have dual-boot where in MS Windows my laptop is really cold, and fans turn on rarely.
P.P.S. Installation of propietary ATI/AMD drivers doesn't works for me.