Documentation/sgi-ioc4.txt - linux-imx - Git at Google

 ====================================
 SGI IOC4 PCI (multi function) device
 ====================================

 The SGI IOC4 PCI device is a bit of a strange beast, so some notes on
 it are in order.

 First, even though the IOC4 performs multiple functions, such as an
 IDE controller, a serial controller, a PS/2 keyboard/mouse controller,
 and an external interrupt mechanism, it's not implemented as a
 multifunction device.  The consequence of this from a software
 standpoint is that all these functions share a single IRQ, and
 they can't all register to own the same PCI device ID.  To make
 matters a bit worse, some of the register blocks (and even registers
 themselves) present in IOC4 are mixed-purpose between these several
 functions, meaning that there's no clear "owning" device driver.

 The solution is to organize the IOC4 driver into several independent
 drivers, "ioc4", "sgiioc4", and "ioc4_serial".  Note that there is no
 PS/2 controller driver as this functionality has never been wired up
 on a shipping IO card.

 ioc4
 ====
 This is the core (or shim) driver for IOC4.  It is responsible for
 initializing the basic functionality of the chip, and allocating
 the PCI resources that are shared between the IOC4 functions.

 This driver also provides registration functions that the other
 IOC4 drivers can call to make their presence known.  Each driver
 needs to provide a probe and remove function, which are invoked
 by the core driver at appropriate times.  The interface of these
 IOC4 function probe and remove operations isn't precisely the same
 as PCI device probe and remove operations, but is logically the
 same operation.

 sgiioc4
 =======
 This is the IDE driver for IOC4.  Its name isn't very descriptive
 simply for historical reasons (it used to be the only IOC4 driver
 component).  There's not much to say about it other than it hooks
 up to the ioc4 driver via the appropriate registration, probe, and
 remove functions.

 ioc4_serial
 ===========
 This is the serial driver for IOC4.  There's not much to say about it
 other than it hooks up to the ioc4 driver via the appropriate registration,
 probe, and remove functions.
	====================================
	SGI IOC4 PCI (multi function) device
	====================================

	The SGI IOC4 PCI device is a bit of a strange beast, so some notes on
	it are in order.

	First, even though the IOC4 performs multiple functions, such as an
	IDE controller, a serial controller, a PS/2 keyboard/mouse controller,
	and an external interrupt mechanism, it's not implemented as a
	multifunction device. The consequence of this from a software
	standpoint is that all these functions share a single IRQ, and
	they can't all register to own the same PCI device ID. To make
	matters a bit worse, some of the register blocks (and even registers
	themselves) present in IOC4 are mixed-purpose between these several
	functions, meaning that there's no clear "owning" device driver.

	The solution is to organize the IOC4 driver into several independent
	drivers, "ioc4", "sgiioc4", and "ioc4_serial". Note that there is no
	PS/2 controller driver as this functionality has never been wired up
	on a shipping IO card.

	ioc4
	====
	This is the core (or shim) driver for IOC4. It is responsible for
	initializing the basic functionality of the chip, and allocating
	the PCI resources that are shared between the IOC4 functions.

	This driver also provides registration functions that the other
	IOC4 drivers can call to make their presence known. Each driver
	needs to provide a probe and remove function, which are invoked
	by the core driver at appropriate times. The interface of these
	IOC4 function probe and remove operations isn't precisely the same
	as PCI device probe and remove operations, but is logically the
	same operation.

	sgiioc4
	=======
	This is the IDE driver for IOC4. Its name isn't very descriptive
	simply for historical reasons (it used to be the only IOC4 driver
	component). There's not much to say about it other than it hooks
	up to the ioc4 driver via the appropriate registration, probe, and
	remove functions.

	ioc4_serial
	===========
	This is the serial driver for IOC4. There's not much to say about it
	other than it hooks up to the ioc4 driver via the appropriate registration,
	probe, and remove functions.