a.f90

module a
contains
    real(q) function foo(y, z)
        use c
        real(q) :: y
        type(c_foo) :: z

        foo = y
    end function foo
end module a 

b.f90

module b
    integer, parameter :: q = selected_real_kind(10)
end module b

c.f90

module c
    use b, only: q

    type :: c_foo
        real(q) :: foo
    end type
end module c