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Linux/Documentation/sgi-ioc4.txt

  1 The SGI IOC4 PCI device is a bit of a strange beast, so some notes on
  2 it are in order.
  3 
  4 First, even though the IOC4 performs multiple functions, such as an
  5 IDE controller, a serial controller, a PS/2 keyboard/mouse controller,
  6 and an external interrupt mechanism, it's not implemented as a
  7 multifunction device.  The consequence of this from a software
  8 standpoint is that all these functions share a single IRQ, and
  9 they can't all register to own the same PCI device ID.  To make
 10 matters a bit worse, some of the register blocks (and even registers
 11 themselves) present in IOC4 are mixed-purpose between these several
 12 functions, meaning that there's no clear "owning" device driver.
 13 
 14 The solution is to organize the IOC4 driver into several independent
 15 drivers, "ioc4", "sgiioc4", and "ioc4_serial".  Note that there is no
 16 PS/2 controller driver as this functionality has never been wired up
 17 on a shipping IO card.
 18 
 19 ioc4
 20 ====
 21 This is the core (or shim) driver for IOC4.  It is responsible for
 22 initializing the basic functionality of the chip, and allocating
 23 the PCI resources that are shared between the IOC4 functions.
 24 
 25 This driver also provides registration functions that the other
 26 IOC4 drivers can call to make their presence known.  Each driver
 27 needs to provide a probe and remove function, which are invoked
 28 by the core driver at appropriate times.  The interface of these
 29 IOC4 function probe and remove operations isn't precisely the same
 30 as PCI device probe and remove operations, but is logically the
 31 same operation.
 32 
 33 sgiioc4
 34 =======
 35 This is the IDE driver for IOC4.  Its name isn't very descriptive
 36 simply for historical reasons (it used to be the only IOC4 driver
 37 component).  There's not much to say about it other than it hooks
 38 up to the ioc4 driver via the appropriate registration, probe, and
 39 remove functions.
 40 
 41 ioc4_serial
 42 ===========
 43 This is the serial driver for IOC4.  There's not much to say about it
 44 other than it hooks up to the ioc4 driver via the appropriate registration,
 45 probe, and remove functions.

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