NEWBIE: how to change serial device<->port association

[Pazzo Da Legare <pazzodalegare@gmail.com>]

Dear ML,

how can I instruct the kernel (if possible) to map a certain serial
port to a specific device ttySx?
I have 4 16550 ports and kernel ( the driver, I suppose) say to me:

Serial: 8250/16550 driver $Revision: 1.90 $ 6 ports, IRQ sharing disabled
serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
serial8250: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A
serial8250: ttyS2 at I/O 0x3e8 (irq = 4) is a NS16550A
serial8250: ttyS3 at I/O 0x2e8 (irq = 3) is a NS16550A
00:08: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
00:09: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A
00:0b: ttyS2 at I/O 0x3e8 (irq = 10) is a NS16550A
00:0c: ttyS3 at I/O 0x2e8 (irq = 11) is a NS16550A

I would like to change the map ttySx -> I/O port. I try with setserial
but it doesn't work....Any clue?

TIA

p