[i2c] [RFC] Rework of i2c-mpc.c - Freescale i2c driver

Matt Sealey matt at genesi-usa.com
Tue Nov 6 19:53:11 CET 2007


Jean Delvare wrote:
> On Mon, 05 Nov 2007 21:52:06 +0000, Matt Sealey wrote:
>> Well, all i2c devices have a chip id you can probe for (...)
> 
> This statement is completely incorrect. I2C devices do NOT have
> standard ID registers. Some devices have proprietary ID registers, some
> don't, it's really up to the manfacturer.

All I2C slave devices have to have a 7- or 10-bit address to identify them
by. They *may* not report what they ARE, but this is 9 times out of
10 a hardware design decision of soldering the chip to a board and
the address is then coded into device trees or hardcoded into drivers.

Whoever designed the board and has the datasheets knows the address
they're supposed to be at, and the device can accept this.

You simply cannot entertain an i2c bus with "anonymous and unnumbered
devices", every one has to have an address it responds to, however
it is defined, or it just does not work.

WRT cell-index this is an index of the bus on the chip (not the logical
i2c bus but the physical difference between two i2c controllers) and
then any i2c devices which need to be communicated with would be
child nodes, their reg property reflecting their slave address, is
that not correct?

-- 
Matt Sealey <matt at genesi-usa.com>
Genesi, Manager, Developer Relations



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