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

[Lee Jones]

On 13/06/12 06:40, Linus Walleij wrote:
> On Tue, Jun 12, 2012 at 9:34 AM, Lee Jones<lee.jones@xxxxxxxxxx>  wrote:
> > On 11/06/12 21:37, Linus Walleij wrote:
> > > So why don't we create proper device tree bindings for the above platform
> > > data?
> > > (...)
> > > This looks to me like a way to push the burden of doing the real
> > > device tree binding for the above to the next user.
> > > (Which will likely be me, so therefore I care a bit ...)
> >
> >
> > On the contrary. This will avoid any added Device Tree complexity and ensure
> > that no extra vendor specific bindings are required. When a new user wishes
> > to use the driver, all they (you) have to do is create a new struct with the
> > platform specific information and add the entry to nmk_gpio_match[],
> > simples.
> >
> > I've even added the logic to extract any information you provide via
> > nmk_gpio_match[] for use as platform data. This keeps it both out of
> > platform code and the Device Tree binary. Everyone's a winner. :)
>
> No. You assume that the platform data is a chip-specific property,
> and that it will be the same for all busses on the chip. But it
> isn't.
>
> The above platform data is *board specific*, it depends on
> what devices have been connected to each bus.
>
> For example the max frequency: this depends on the maximum
> frequency any of the devices connected to one very bus
> can support.
>
> The other platforms have put this frequency into their device
> trees for a reason, and this is it.
>
> So for the four different i2c busses there may need to be
> four different platform data sets. How are you going to
> distinguish between the four buses?
>
> This is thus broken and needs to have proper bindings.

Board specific is fine, as the data is protected by a board specific 
property. Do you mean that the properties are *bus specific*? In which 
case I see your point and will apply the correct bindings.

--
Lee Jones
Linaro ST-Ericsson Landing Team Lead
M: +44 77 88 633 515
Linaro.org â Open source software for ARM SoCs
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