Enumerable I2C busses

[Rafał Jaworowski]

On 2008-11-23, at 19:18, Dag-Erling Smørgrav wrote:

> Nathan Whitehorn <nwhitehorn at freebsd.org> writes:
>> The current I2C bus mechanism does not support the bus adding its own
>> children [...]
>
> That's because the I2C protocol does not support device enumeration or
> identification.  You have to know in advance what kind of devices are
> attached and at what address.  Even worse, it is not uncommon for
> similar but not entirely compatible devices to use the same I2C  
> address
> (for instance, every I2C-capable RTC chip uses the same address, even
> though they have different feature sets)

Well, hard-coded addresses and conflicting assignments between vendors  
do not technically prevent from scanning the bus; actually, our  
current iicbus code can do bus scaning when compiled with a diag  
define. The problem however is some slave devices are not well- 
behaved, and they don't like to be read/written to other than in very  
specific scenario: if polled during bus scan strange effects occur  
e.g. they disappear from the bus, or do not react to consecutive  
requests etc.

Nathan, not sure if this helps you, but I have a nice i2c diagnostic  
tool, which among other features lets the user scan the I2C bus for  
present slave devices. This is done from userland, so doing similar  
thing in-kernel wouldn't be a problem. I was planning to post this for  
review this coming week, so you can have a look.

Rafal