devc-ser8250 Hardware Handshake Lines

I’m interfacing with another embedded device through a 16550 uart using
RTS/CTS for flow control. I found out the hard way that when using hardware
handshaking with devc-ser8250 that the state of DCD (and to a lesser extent
DSR) can have a drastic impact on the driver’s receiver efficiency (from 11%
cpu utilization to 70%). Is there a way to tell the driver to ignore DCD and
DSR while still using RTS/CTS, or must I make sure that those signals are

I see from the 16550 datasheet that the interrupts for DCD and DSR cannot be
masked independently of the CTS interrupt. I suppose it’s possible that
these inputs are toggling state while floating, thus generating lots of
interrupts, but I would not expect that. Is there some other driver overhead
that non-asserted DCD and DSR inputs causes?

Marty Doane