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

Scott Wood scottwood at freescale.com
Tue Nov 6 08:55:43 EST 2007

Matt Sealey wrote:
> Scott Wood wrote:
>> Jon Smirl wrote:
>>>>> cell-index = <1>;
>>>> What is cell-index for?
>>> I was using it to control the bus number, is that the wrong
>>> attribute?
>> It shouldn't be specified at all -- the hardware has no concept of
>> a device number.
> Well, all i2c devices have a chip id you can probe for,

I meant a controller device number (a.k.a. bus number), which (outside 
of documentation) is purely a Linux invention, and which is what 
cell-index was being used for above.

> as for buses I think cell-index is a holdover from the way the PSC
> code is organised on the MPC5200 for example - if you have multiple
> buses which use the same registers, for example. It's redundant on
> the PSC's for programming because they all use different register
> offsets but if you move to other devices like the GPTs, then it is
> then useful for debugging (it is far more interesting to say GPT1
> than GPT @ offset to match the) and in general for tweaking OTHER
> parts of the chip (for instance the CDM - very relevant!) which use
> single registers to control entire swathes of units.

Right, that's what cell-index is for.  This is different. :-)


More information about the Linuxppc-dev mailing list