[i2c] [PATCH 2/2] i2c: Add devtree-aware iic support for PPC4xx

Scott Wood scottwood at freescale.com
Mon Oct 15 21:54:39 CEST 2007


Grant Likely wrote:
> On 10/15/07, Scott Wood <scottwood at freescale.com> wrote:
>> For associating a device node with a human readable label, I'd
>> prefer a "label" property in the device node, rather than doing it
>> backwards with aliases.
> 
> Here the corresponding problem; having to scan every device node to 
> make sure you don't assign a number already selected by another node 
> (in the case where one node is assigned a number and another is not).
> 
Don't Do That(tm).  If you use this mechanism, and an adapter node
doesn't have a bus number, then it doesn't get to pre-register devices,
but instead must use i2c_new_device.

>>> As per your point below; if all the i2c devices are children of
>>> the adapter, then yes you are right that the bus number doesn't
>>> matter to the user.  But it *does* matter for things like serial
>>> and ethernet ports.
>> And a label property would be great for that. :-)
> 
> Not really; if the user needs to renumber devices; you don't want him
>  fiddling around in the hardware description.

Why would the user renumber devices?

> Just like the chosen node; an aliases describes logical constructs,
> not physical ones.  I don't think this is any different from the
> linux,stdout-path property in chosen.

Well, it's somewhat different in that stdout describes a usage of the 
device, not the identity.

Still, I don't like linux,stdout-path. :-)
At the very least it should be a phandle.

-Scott



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