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diff --git a/Documentation/sgi-ioc4.txt b/Documentation/sgi-ioc4.txt new file mode 100644 index 000000000..72709222d --- /dev/null +++ b/Documentation/sgi-ioc4.txt @@ -0,0 +1,49 @@ +==================================== +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. |