Red Hat's Matthew Garrett has actively been working on improving power management with graphics processors via the various open-source X.Org drivers. There is quite a lot of work involved, but at the FOSDEM X.Org meeting he shared an update on his progress. In particular, Matthew is trying to conserve power with the GPU, memory, outputs, and displays.
To save power on the GPU core he has been attempting to implement clock-gating and re-clocking support in the different drivers while to reduce the memory power consumption he has been hacking away at frame-buffer compression and re-clocking. When it comes to outputs, most of his power conservation work has dealt with load detection and shutting down PLLs when not in use. Lastly, to conserve power with the display, Garrett sees possibilities in LVDS re-clocking and DPMS (Display Power Management Signaling).
Matthew Garrett is looking at aggressive dynamic state management and demand-based functionality as other areas to work on as part of his GPU power management code. The progress of his work though has been varying based upon what's supported by the different X.Org drivers and the specifications he has access to from the different vendors.