regarding device driver

Hi All,
I have a device driver that uses UARTserial port to write/read to-from a device.
That device driver is working fine on FC3 machine( kernel version 2.6.12)...
Now I am switching to FC9 (kernel version 2.6.25.11-97).I have changed the interrupt flag SA_INTERRUPT to IRQF_DISABLED for FC9.
device driver is compiling & loading properly.My program is able to send the data as well as device is also responding but I m not able to get the data inside the PC.According to me ,recieve data line interrupt is not able to get CPU attention in properly time.may be I have to increase the priority of IRQ4.
so plz tell me how to increase the priority of IRQ4 in FC9 or any other solutuion...
Thnx in advance....