We use an array of iOS apps (LIDO mPilot, eWas for example) that greatly benefit from having a GPS information sent to them.
As sad as it is, the 787's built-in EFB is a disgrace to both Technology (poor quality touch screen, very sluggish processor) and Ergonomy (very poor placement, way out of sight and reach).
I did find a sweet spot where signal is acquired :
Bottom left of captain's side window, rearest area of the indentation, top of the climbing slope.