2.4.21-pre4 / IrDA on a Dell C640, still no go

I've had a bit more time to try the smsc-ircc2 driver, but as
its predecessor it fails to find an irq for the chip (LPC47N252), printing out

IrCC version 2.0, firport 0x290, sirport 0x3e8, dma=3, irq=0

I tried booting into Win2K, where the driver claims to be using
irq 3, rebooted in 2.4.21-pre4, said

[root@incident root]# insmod smsc-ircc2 ircc_irq=3

but apart from getting a printk saying

smsc-ircc2, Overriding IRQ - chip says 0, using 3

I still see nothing doing irdadump, and /proc/interrupts only
shows these:

  0:   324401      XT-PIC  timer
  1:     3592      XT-PIC  keyboard
  2:        0      XT-PIC  cascade
  9:        5      XT-PIC  acpi
 11:        0      XT-PIC  Intel ICH3, Texas Instruments PCI1420,
       Texas Instruments PCI1420 (#2), usb-uhci
 12:        6      XT-PIC  PS/2 Mouse
 14:     3987      XT-PIC  ide0
 15:        0      XT-PIC  ide1

There is no option in the Dell BIOS to choose an IRQ for the
IR chip (as it isn't there in this CPx750J, but this one works just fine on irq 4).

Any suggestion on how to go on from here is welcome !

Thanks, ciao,

--alessandro