Documentation/i2c/busses/i2c-piix4

Kernel driver i2c-piix4

Supported adapters:
  * Intel 82371AB PIIX4 and PIIX4E
  * Intel 82443MX (440MX)
    Datasheet: Publicly available at the Intel website
  * ServerWorks OSB4, CSB5, CSB6 and HT-1000 southbridges
    Datasheet: Only available via NDA from ServerWorks
  * ATI IXP southbridges IXP200, IXP300, IXP400
    Datasheet: Not publicly available
  * Standard Microsystems (SMSC) SLC90E66 (Victory66) southbridge
    Datasheet: Publicly available at the SMSC website http://www.smsc.com

Authors: 
	Frodo Looijaard <frodol@dds.nl>
	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!
* fix_hstcfg: int
  Fix config register. Needed on some boards (Force CPCI735).


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...

Do 'lspci -v' and see whether it contains an entry like this:

0000:00:02.3 Bridge: Intel Corp. 82371AB/EB/MB PIIX4 ACPI (rev 02)
	     Flags: medium devsel, IRQ 9

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, the Intel 440MX, and the Victory766 are
identical to the PIIX4 in I2C/SMBus support.

A few OSB4 southbridges are known to be misconfigured by the BIOS. In this
case, you have you use the fix_hstcfg module parameter. Do not use it
unless you know you have to, because in some cases it also breaks
configuration on southbridges that don't need it.