Anyone have much to do with QoS on Cisco Catalysts?

I am getting a little confused. I have a switch which has three ports
+ an uplink port which carries VoIP, I want those ports to get
Sounds simple right? To make it even easier the device that is
attached to the three ports assigns a CoS, so I can from my
understanding set the switch to trust that CoS rather than recalculate

Now in their little QoS flow chart of setting up QoS it indicates that
you assign the label (Classification) -> Policing -> Mark -> Queueing
and Scheduling

Do I really need to set up the 'Policing' and 'Mark'? Or can I simply
go to the Queueing and Scheduling as we already have a CoS?