Paulo Zanoni wrote in the patch series, "Intermediate Pixel Storage is a feature that should reduce the number of times the display engine wakes up memory to read pixels, so it should allow deeper PC states. IPS can only be enabled on ULT pipe A with 8:8:8 pipe pixel formats."
The difference in sleep states when using Intermediate Pixel Storage should be quite noticeable. "With eDP 1920x1080 and correct watermarks but without FBC this moves my PC7 residency from 2.5% to around 38%."
The FBC feature talked about is Frame-Buffer Compression and should also lead to letting the CPU/GPU sleep longer. Hopefully the IPS support will be primed and ready for merging with FBC into the Linux 3.11 kernel.