When we tried to update REDMI 2 PRIME from Android(kitkat)4.4.4 to Lollipop 5.1.1 by using CMW recovery, I have got proximity sensor issue (Screen complete black out when calling out and in) in Lollipop. I have used Nexus Experience - Official Release 9.8.3. (Link: http://en.miui.com/thread-167703-1-1.html)
I found solution to fix it 100 percent. There are three steps do it. Follow the video.
How to Root Redmi 2 without PC: Video
How to install CMW recovery in Redmi 2 without PC(ENG and Telugu): Video
Sensor file download here:
Android5.1.1 Rom download here:
NX GAPPS: download here