Comment 85 for bug 563156

after upgrading to 10.10 and switching back to the opensource driver nothing changed, temp still > 70° and fan was always running.
I know that the new kernel 2.6.35.x has some radeon specific powersaving features implemented, after searching a bit I've found the relevant information. It seems that the default powerprofile is the high one.
It is possible to override this, check the power method:
cat /sys/class/drm/card0/device/power_method
=> should be profile
echo auto > /sys/class/drm/card0/device/power_profile
=> enables auto profile switching, low on bat, high on AC
now check the GPU frequ:
  cat /sys/kernel/debug/dri/0/radeon_pm_info
default engine clock: 550000 kHz
current engine clock: 219370 kHz
default memory clock: 800000 kHz
current memory clock: 249750 kHz
voltage: 900 mV
PCIE lanes: 16

after setting the profile to auto, temp. goes down immediately.

For more detailed description of the power saving functions look at: