[i2c] [PATCH 3/5] powerpc: Document device nodes for I2C devices.

[Kumar Gala]

On May 18, 2007, at 11:31 AM, Jean Delvare wrote:

> On Fri, 18 May 2007 10:58:06 -0500, Scott Wood wrote:
>> Jean Delvare wrote:
>>> On Thu, 17 May 2007 14:32:11 -0500, Scott Wood wrote:
>>>
>>>> (and the
>>>> i2c code in Linux should be fixed to allow drivers to specify  
>>>> multiple
>>>> match names).
>>>
>>>
>>> Back when David proposed his new-style i2c code, I had the same
>>> objection. But we addressed the need differently. If you look at  
>>> struct
>>> i2c_board_info, you'll see two string fields, driver_name and  
>>> type. The
>>> former specifies the driver name, the second specifies the exact  
>>> device
>>> variant. For drivers which support several device variants, the
>>> platform code should fill both fields.
>>
>> But that still requires the platform to know the driver name, rather
>> than matching any driver which knows about the type.  This  
>> prevents the
>> use of OS-independent device trees (such as in Open Firmware), which
>> cannot know specific Linux driver names, without something hacky  
>> like a
>> type-to-driver table in the device tree code.
>
> Oh well, this was also the reason why I objected to David's  
> approach in
> the first place. If you dig back in the i2c list archive, you'll find
> that I was asking for exactly the same thing you do now: that each i2c
> driver would export a list of supported devices, and the i2c-core  
> would
> match a device name against that list (independent of the driver  
> name.)
> It felt more flexible, but I wondered how useful it would be in
> practice, and finally gave up and David had the last word. If you had
> shown up back then rather than now...
>
> I am not familiar with Open Firmware. How standard is it? How  
> realistic
> would it be to use their device naming in the Linux kernel? Are there
> other subsystem doing this? Are there other OSes using it, in
> particular for I2C?

OF doesn't have any particular bindings that already exist for I2C.   
If it had I might be more in favor of trying to make Linux work with it.

Here's a link to give you some idea of what bindings exist already  
for OF:

http://openbios.info/Bindings

> We have something which works now, even if that's not what you and I
> had in mind, so I don't really want to change it without solid  
> reasons.

agreed.

- k