When it comes to ATI open-source power management, so far AMD's open-source kindness
has just yielded a list of registers but no proper documentation or how PowerPlay
exactly works. However, AMD's Alex Deucher has just committed "Dynamic Clocks" support for the Radeon R500 and R600 graphics cards. Dynamic Clocks just provides dynamic clock gating and static power management, permitting the graphics card supports this capability. With some graphics cards it's already been setup through the video BIOS, so today's work isn't relevant to everyone. Dynamic Clocks is not nearly as elaborate as PowerPlay, but it's a good start for the xf86-video-ati driver.
Check out the xf86-video-ati git tree at FreeDesktop.org
if you're a mobile or desktop user looking for improved power management through an open-source driver on R500/600 hardware.