Intel Linux developers are still working on a Haswell run-time power management feature for their open-source graphics driver.
Paulo Zanoni published a set of 19 patches this week that provide Haswell run-time power management support for putting the graphics device into a D3 power-savings state. While Haswell has been out for months and the developers are already working on Broadwell, this Haswell PM feature is only coming after the developers had been working on similar support for Bay Trail / Valley View graphics.
This runtime power management support can be enabled by writing "auto" to a new sysfs file for the Intel DRM graphics driver. While the 19 patches are out there now changing several hundred lines of code, still to be worked on for this patch-set is merging PC8 and runtime D3, support for PC8/D3 on DPMS (Display Power Management Signalling), and support for other platforms (including possibly Ivy Bridge).
The Intel Haswell runtime power management feature will hopefully be merged for the Linux 3.14 kernel; many more details can be found from the mailing list patch-set