Knee torque of a lumped mass model

Consider the planar legged model depicted to the right. The robot's mass is concentrated at its center of mass \(G\), meaning we neglect the mass of the two links of the leg. The center of mass is located above the center of pressure \(C\) and the robot is in static equilibrium. The leg has a single revolute joint located at the knee \(K\) with joint angle \(q\). Both of its links have the same length \(CK = KG = \ell\).

Question: what is the joint torque \(\tau\) exerted by the knee to keep the leg in static equilibrium?