This commit was manufactured by cvs2svn to create branch 'vserver'.

[linux-2.6.git] / Documentation / i2c / busses / i2c-piix4

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+Kernel driver i2c-piix4
+
+Supported adapters:
+  * Intel 82371AB PIIX4 and PIIX4E
+  * Intel 82443MX (440MX)
+    Datasheet: Publicly available at the Intel website
+  * ServerWorks OSB4, CSB5 and CSB6 southbridges
+    Datasheet: Only available via NDA from ServerWorks
+  * 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.