Re: [PATCH 09/14] i2c: Add Device Tree support to the Nomadik I2Cdriver

[Lee Jones]

On 15/06/12 11:32, Russell King - ARM Linux wrote:
> 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...

Right. See my most recent emails on the subject. :)

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Lee Jones
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Linaro.org â Open source software for ARM SoCs
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