Kernel driver `i2c-piix4.o'

Status: Complete and well-tested

Supported adapters:
  * Intel 82371AB PIIX4 and PIIX4E
  * Intel 824443MX (440MX)
    Datasheet: Publicly available at the Intel website
  * ServerWorks OSB4 and CSB5 southbridges
    Datasheet: Only available via NDA from ServerWorks

Author: Frodo Looijaard <frodol@dds.nl> and Philip Edelbrock
        <phil@netroedge.com>


Module Parameters
-----------------

* force: int
  Forcibly enable the PIIX4. DANGEROUS!
* force_addr: int
  Forcibly enable the PIIX4 at the given address. EXTREMELY DANGEROUS!


Description
-----------

The PIIX4 (properly known as the 82371AB) is an Intel chip with a lot of
functionality. Among other things, it implements the PCI bus. One of its
minor functions is implementing a System Management Bus. This is a true 
SMBus - you can not access it on I2C levels. The good news is that it
natively understands SMBus commands and you do not have to worry about
timing problems. The bad news is that non-SMBus devices connected to it
can confuse it mightily. Yes, this is known to happen...

Cat /proc/pci, and see whether it contains an entry like this:

  Bus  0, device   1, function  3:
    Bridge: Intel 82371AB PIIX4 ACPI (rev 1).
      Medium devsel.  Fast back-to-back capable.  

Bus and device numbers may differ, but the function number must be identical
(like many PCI devices, the PIIX4 incorporates a number of different
'functions', which can be considered as separate devices). If you find such
an entry, you have a PIIX4 SMBus controller.

On some computers (most notably, some Dells), the SMBus is disabled by
default. If you use the insmod parameter 'force=1', the kernel module
 will try to enable it. THIS IS VERY DANGEROUS! If the BIOS did not
set up a correct address for this module, you could get in big trouble
(read: crashes, data corruption, etc.). Try this only as a last resort
(try BIOS updates first, for example), and backup first! An even more
dangerous option is 'force_addr=<IOPORT>'. This will not only enable the
PIIX4 like 'force' foes, but it will also set a new base I/O port address.
The SMBus parts of the PIIX4 needs a range of 8 of these addresses to
function correctly. If these addresses are already reserved by some other
device, you will get into big trouble! DON'T USE THIS IF YOU ARE NOT VERY
SURE ABOUT WHAT YOU ARE DOING!

The PIIX4E is just an new version of the PIIX4; it is supported as well. The
PIIX/PIIX3 does not implement an SMBus or I2C bus, so you can't use this
driver on those mainboards.

The ServerWorks Southbridges and the Intel 440MX are identical
to the PIIX4 in I2C/SMBus support.