This applies only when the user manually instantiates the stratixv_mac component (i.e., WYSIWYG flow).
You will get the above error if the "chainin" port is present on the stratixv_mac instantiation but it is not connected to the chainout port of another DSP block. You may also get this error if the "use_chainadder" generic is "true" when the chainin port is unused.
Intel® Quartus® is expecting the chainin port to be either disconnected (not present), or connected to the chainout of another DSP block. Connecting chainin to a fixed value (0, 1, X, Z) does not count as being disconnected. Quartus also expects "use_chainadder" to be "false" if chainin is not used.
To resolve this issue, either disconnect the chainin port entirely and set use_chainadder="false".