Hi Shwetank,
Here is my understanding so far on how these modules should easily be integrated:
Supply run is triggered by Consensus Demand which should be the outcome of Demand Review step of S&OP process, reconciliation between statistical and financial driven demand.
Inventory has as input key figure the Inventory Forecast, which can hold a sensed demand (based current realities of a supply chain - like sales orders) or the demand planning qty. Recommended safety stock is one of the output key figures of Inventory modules which goes as input in the Supply run.
These points should be more clarified with the release of the new planning area which will provide E2E visibility...so looking forward to it 
Input Key Figures for Inventory - SAP Integrated Business Planning - SAP Library
Regards
Alecsandra