  We report on our ongoing determination of the charm quark mass and the masses
and decay constants of various charmed mesons, obtained within a mixed-action
setup. We employ $N_f=2+1$ CLS ensembles combined with a Wilson twisted mass
valence action that eliminates the leading $O(a)$ effects from our target
observables. Alongside our preliminary results, we will discuss an exploration
of GEVP techniques aimed at optimizing the precision in view of the extension
of the computation to heavier quark masses. We study the chiral-continuum
extrapolation of decay constants for charm quark observables and the
renormalized charm quark mass.
