vlv_force_gfx_clock
err = vlv_force_gfx_clock(dev_priv, true);
err = vlv_force_gfx_clock(dev_priv, false);
vlv_force_gfx_clock(dev_priv, false);
ret = vlv_force_gfx_clock(dev_priv, true);
err = vlv_force_gfx_clock(dev_priv, false);
int vlv_force_gfx_clock(struct drm_i915_private *dev_priv, bool on);