Merge branch 'i2c-for-linus' of git://jdelvare.pck.nerim.net/jdelvare-2.6

* 'i2c-for-linus' of git://jdelvare.pck.nerim.net/jdelvare-2.6:
  i2c-core: Some style cleanups
  i2c-piix4: Add support for the Broadcom HT1100 chipset
  i2c-piix4: Add support to SB800 SMBus changes
  i2c-pca-platform: Use defaults if no platform_data given
  i2c-algo-pca: Use timeout for checking the state machine
  i2c-algo-pca: Rework waiting for a free bus
  i2c-algo-pca: Add PCA9665 support
  i2c: Adapt debug macros for KERN_* constants
  i2c-davinci: Fix timeout handling
  i2c: Adapter timeout is in jiffies
  i2c: Set a default timeout value for all adapters
  i2c: Add missing KERN_* constants to printks
  i2c-algo-pcf: Handle timeout correctly
  i2c-algo-pcf: Style cleanups
  eeprom/at24: Remove EXPERIMENTAL
  i2c-nforce2: Add support for MCP67, MCP73, MCP78S and MCP79
  i2c: Clarify which clients are auto-removed
  i2c: Let checkpatch shout on users of the legacy model
  i2c: Document the different ways to instantiate i2c devices

1 files changed, 15 insertions, 4 deletions

diff --git a/Documentation/i2c/writing-clients b/Documentation/i2c/writing-clients
index 6b9af7d479c..c1a06f989cf 100644
--- a/Documentation/i2c/writing-clients
+++ b/Documentation/i2c/writing-clients
@@ -207,15 +207,26 @@ You simply have to define a detect callback which will attempt to
 identify supported devices (returning 0 for supported ones and -ENODEV
 for unsupported ones), a list of addresses to probe, and a device type
 (or class) so that only I2C buses which may have that type of device
-connected (and not otherwise enumerated) will be probed.  The i2c
-core will then call you back as needed and will instantiate a device
-for you for every successful detection.
+connected (and not otherwise enumerated) will be probed.  For example,
+a driver for a hardware monitoring chip for which auto-detection is
+needed would set its class to I2C_CLASS_HWMON, and only I2C adapters
+with a class including I2C_CLASS_HWMON would be probed by this driver.
+Note that the absence of matching classes does not prevent the use of
+a device of that type on the given I2C adapter.  All it prevents is
+auto-detection; explicit instantiation of devices is still possible.
 
 Note that this mechanism is purely optional and not suitable for all
 devices.  You need some reliable way to identify the supported devices
 (typically using device-specific, dedicated identification registers),
 otherwise misdetections are likely to occur and things can get wrong
-quickly.
+quickly.  Keep in mind that the I2C protocol doesn't include any
+standard way to detect the presence of a chip at a given address, let
+alone a standard way to identify devices.  Even worse is the lack of
+semantics associated to bus transfers, which means that the same
+transfer can be seen as a read operation by a chip and as a write
+operation by another chip.  For these reasons, explicit device
+instantiation should always be preferred to auto-detection where
+possible.
 
 
 Device Deletion