We recommend that the QoS policy on the router/switch interfaces connected to the WLC be set to trust the CoS settings of the WLC. This means that the wired network responds to the CoS values controlled by the QoS policy set on the WLC. The WLC does not enforce any policy that changes the WLAN client DSCP values. The WLC policy effects will only be seen in the CoS values associated with the WLAN client traffic.
If the routers and switches connecting to the WLC are set to trust DSCP, then a DSCP policy must be created and maintained on those router and switch interfaces--in addition to the policies applied on the WLC. For more information on WLAN QoS and traffic classification, refer to the Chapter 3, "Voice over WLAN Radio Frequency Design".
https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/vowlan/41dg/vowlan41dg-book/vowlan_ch8.html