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The SGI IOC4 PCI device is a bit of a strange beast, so some notes onit are in order.First, even though the IOC4 performs multiple functions, such as anIDE controller, a serial controller, a PS/2 keyboard/mouse controller,and an external interrupt mechanism, it's not implemented as amultifunction device. The consequence of this from a softwarestandpoint is that all these functions share a single IRQ, andthey can't all register to own the same PCI device ID. To makematters a bit worse, some of the register blocks (and even registersthemselves) present in IOC4 are mixed-purpose between these severalfunctions, meaning that there's no clear "owning" device driver.The solution is to organize the IOC4 driver into several independentdrivers, "ioc4", "sgiioc4", and "ioc4_serial". Note that there is noPS/2 controller driver as this functionality has never been wired upon a shipping IO card.ioc4====This is the core (or shim) driver for IOC4. It is responsible forinitializing the basic functionality of the chip, and allocatingthe PCI resources that are shared between the IOC4 functions.This driver also provides registration functions that the otherIOC4 drivers can call to make their presence known. Each driverneeds to provide a probe and remove function, which are invokedby the core driver at appropriate times. The interface of theseIOC4 function probe and remove operations isn't precisely the sameas PCI device probe and remove operations, but is logically thesame operation.sgiioc4=======This is the IDE driver for IOC4. Its name isn't very descriptivesimply for historical reasons (it used to be the only IOC4 drivercomponent). There's not much to say about it other than it hooksup to the ioc4 driver via the appropriate registration, probe, andremove functions.ioc4_serial===========This is the serial driver for IOC4. There's not much to say about itother than it hooks up to the ioc4 driver via the appropriate registration,probe, and remove functions.