The DSCP priority and IP precedence use different bits of the ToS field; therefore, an interface cannot be configured to trust DSCP priorities and IP precedences simultaneously.
The S5720SI, S5720S-SI, S5720LI, S5720S-LI, S5710-X-LI, S1720GW-E, S1720GWR-E, S1720GW, and S1720GWR do not support the trust ip-precedence command.