<clock_name> are timed together but have no phase
relationship. The design could fail in hardware. One of the clocks originates from the
<cell> that is not using the phase detector,
or its incoming clock is not connected to the
CLKIN_DESKEW pin. Under these conditions, it is unsafe to time between the
master clock of the DPLL and its auto-derived clock (or downstream generated clocks)
because the relationship between the clocks is unknown.