While the Radeon R100-R500 series kernel mode-setting support appeared in the Linux 2.6.31 kernel
and DRM patches pending for the Linux 2.6.32 kernel
that bring KMS support for newer hardware and other improvements, the ATI KMS driver is not complete. Features such as power management need to be brought into the kernel driver (for Intel too) where they will be better off compared to the traditional DDX drivers. However, that ATI KMS power management support is now further underway with a set of patches published today to the DRI development list.
Rafał Miłecki has published a set of five patches that adds support for reading clock values (both engine and memory), the ability to store power management states (core and memory clocks along with core voltage), detection support for an ASIC's minimum and maximum clocks, setting the new state (currently only the engine clock support is hooked in), and then lastly is a patch that will automatically down-clock the GPU when the connected display is signaled off by the DPMS (Display Power Management Signaling) support.
This set of patches -- that can be found on the dri-devel list
-- is really just the start of providing proper power management support for ATI Radeon graphics cards within Linux running a free software stack. Additional steps are already being taken to improve Linux GPU power management
such as automatic load detection / usage to dynamically change power states, LVDS re-clocking, and other new functionality.