We present RBC/UKQCD’s charm project usingNf=2+1 flavour ensembles with inverse lat-tice spacings in the range 1.73−2.77 GeV and two physical pion mass ensembles. Domain wallfermions are used for the light as well as the charm quarks. We discuss our strategy for the extrac-tion of the decay constantsfDandfDsand their extrapolation to the continuum limit, physical pionmasses and the physical heavy quark mass. Our preliminary results arefD=208.7(2.8)MeV andfDs=246.4(1.9)MeV where the quoted error is statistical only. We outline our current approach to extend the reach in the heavy quark mass and present preliminary results