  We consider a spin circuit-QED device where a superconducting microwave
resonator is capacitively coupled to a single hole confined in a semiconductor
quantum dot. Thanks to the strong spin-orbit coupling intrinsic to valence-band
states, the gyromagnetic g-matrix of the hole can be modulated electrically.
This modulation couples the photons in the resonator to the hole spin. We show
that the applied gate voltages and the magnetic-field orientation enable a
versatile control of the spin-photon interaction, whose character can be
switched from fully transverse to fully longitudinal. The longitudinal coupling
is actually maximal when the transverse one vanishes and vice-versa. This
"reciprocal sweetness" results from geometrical properties of the g-matrix and
protects the spin against dephasing or relaxation. We estimate coupling rates
reaching ~ 10 MHz in realistic settings and discuss potential circuit-QED
applications harnessing either the transverse or the longitudinal spin-photon
interaction. Furthermore, we demonstrate that the g-matrix curvature can be
used to achieve parametric longitudinal coupling with enhanced coherence.
