So if I boot with "radeon.dpm=1" then, as allready described, the laptop uses
"relatively little" power, and is faning off some heat continuously, even when
I set:

  # echo "battery" > /sys/class/drm/card1/device/power_dpm_state

Whether I do the following does *not* seem to matter:

  # echo IGD > /sys/kernel/debug/vgaswitcheroo/switch
  # echo OFF > /sys/kernel/debug/vgaswitcheroo/switch

But if I boot *without* "radeon.dpm=1" then the laptop will stay cool without
fans running out of the box using around 14W.

The various settings will show this then:

  # cat /sys/class/drm/card1/device/power_method
  dpm
  # cat /sys/class/drm/card1/device/power_profile
  default
  # cat /sys/class/drm/card1/device/power_dpm_state
  balanced

Weird that power_method would show "dpm" even though I have booted *without*
"radeon.dpm=1" ?!

When I then set:

  # echo "battery" > /sys/class/drm/card1/device/power_dpm_state

Power consumption will drop even further to ~11W.

The overal logic of all of this is evidently completely escaping me... 8-o