Subject: Re: [PATCH 3/5] powerpc: Document device nodes for I2C devices.

From: Scott Wood <[email-masked]>
Date: Thu, 17 May 2007 11:47:24 -0500

Kumar Gala wrote:
> On May 17, 2007, at 11:17 AM, Scott Wood wrote:
>> Kumar Gala wrote:
>>> As I've stated before, we need a bus number as well so we can  
>>> handle  things like I2C switches and muxes.
>>
>> Is this something we handle now?  If not, then it's really not  within 
>> the scope of this patchset.  If so, how am I breaking it?
> 
> We don't handle i2c devices in the dev tree today.  If you are going  to 
> propose a solution it should work for all cases that people are  aware 
> of even if linux doesn't support the functionality.

But we do handle i2c *controllers* in the device tree, and that's where 
a bus number property would go.  Given that we don't have a binding for 
non-toplevel i2c buses, and I'm not adding one, I don't see the 
relevance.  Note that adding a bus number property makes zero sense for 
toplevel buses, as at that level the bus number is just a fiction 
maintained by Linux for user API and device preregistration purposes.

It's not a matter of the binding only covering some cases; it's a matter 
of the binding being for one thing (i2c devices) and not another 
(multiplexed i2c buses).

> If only some subset of cases are handled what good is the device tree  
> to a user?  They will just have to figure out if their usage is  
> supported or not and if not find some other solution that works for  them.

...just as they'll have to figure out if a binding exists for device 
type $FOO.

-Scott