Re: [PATCH 09/14] i2c: Add Device Tree support to the Nomadik I2C driver

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Thu, Jun 14, 2012 at 07:57:32PM +0100, Lee Jones wrote:
> On 14/06/12 19:36, Mark Brown wrote:
>> On Wed, Jun 13, 2012 at 01:28:17PM +0100, Lee Jones wrote:
>>
>>> Device Tree. However, we have just as much control by keeping them
>>> in separate structs in the C file and selecting the right one using
>>> the compatible sting.
>>
>> You're not understanding Linus' point.  The compatible string isn't
>> useful here because properties like the maximum clock rate of the bus
>> depend on the board design, not the silicon.  The controller may be
>> perfectly happy to run at a given rate but other devices on the bus or
>> the electrical engineering of the PCB itself may restrict this further.
>
> And you're not understanding mine. ;)
>
> You can have multiple compatible strings for a single driver. Which one  
> you reference from the Device Tree will dictate which group of settings  
> are used, including variation of clock rates.

However, if you list these settings separately, rather than selecting them
based on a compatible string, it means when other board designs come along,
you don't have to modify the kernel code to provide yet another compatible
to settings translation in the code - you can keep all that information
entirely within DT with no kernel code mods.

I thought that was partly the point of DT...