Recently, I am busy with project based on mini2440 board. I use two pcf8574 chips whitch connect to i2c bus to expand digital IO, 8 bits as input , 8 bits as output. I find that linux contains the pcf8574 driver .And I add this driver into the kernel. But I can't find the file innod in /dev folder. My question is how to use this driver to operate the device?