drivers for opencores 16550 Uart

I add opencores 16550 uart to nios2.

Then I'd like to use it in linux.

I found these files about the driver 8250/16550:

<kernel>/drivers/sierial/8250.c; 8250.h

<kernel>/include/linux/serial.h; serial_8250.h; serial_core.h; serial_reg.h

But I can&#39;t to figure out how to let the driver know the real HW address, i.e. na_uart1?

If there are na_uart1,na_uart2, na_uart3... 4 * uarts in my systems, how to deal with in the drivers?