The S3300, S5300, or S6300 interface can be configured to trust DSCP priorities and 802.1p priorities or trust IP precedences and 802.1p priorities. When an interface is configured to trust DSCP priorities, IP precedences, and 802.1p priorities, the interface:

•  Trusts DSCP priorities or IP priorities if IP packets are received.
•  Trusts 802.1p priorities if non-IP packets are received.

        The DSCP priority and IP precedence use different bits of the ToS field; therefore, an interface cannot be configured to trust dscp and trust ip-precedence.
        The S5300HI supports the trust dscp, trust 8021p inner, and trust 8021p outer commands, but these commands cannot be used simultaneously.

very clear and easy to understand

Thank you!