Question

Access to all objects declared in an interface is always available by hierarchical reference, regardless of whether or not the interface is connected through a port. When an interface is connected with a modport in either the module header or port connection, access by port reference is limited to only those objects listed in the modport, for only those types of objects legal to be listed in modports (nets, variables, tasks, and functions) All objects are still visible by hierarchical reference. For example:

interface ebus_i;
    integer I; // reference to I not allowed through modport mp
    typedef enum {Y,N} choice;
    choice Q;
    parameter True = 1;
    modport mp(input Q);
endinterface

module Top;
    ebus_i ebus;
    sub s1(ebus.mod);
endmodule

module sub(interface.mp i);
    typedef i.choice yes_no; // import type from interface
    yes_no P;
    assign P = i.Q; // refer to Q with a port reference

    initial
        Top.s1.Q = i.True; // refer to Q with a hierarchical reference

    initial
        Top.s1.I = 0; // referring to i.I would not be legal because
        // is not in modport mp
endmodule