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

[Lee Jones]

On 11/06/12 21:37, Linus Walleij wrote:
> On Mon, Jun 11, 2012 at 5:25 PM, Lee Jones<lee.jones@xxxxxxxxxx>  wrote:
>
> > As new users are
> > added, it is expected that they will be Device Tree compliant.
> > If this is the case, we will look up their initialisation values
> > by compatible entry, then apply them forthwith.
> (...)
> > +static struct nmk_i2c_controller u8500_i2c = {
> > +       /*
> > +        * slave data setup time, which is
> > +        * 250 ns,100ns,10ns which is 14,6,2
> > +        * respectively for a 48 Mhz
> > +        * i2c clock
> > +        */
> > +       .slsu           = 0xe,
> > +       /* Tx FIFO threshold */
> > +       .tft            = 1,
> > +       /* Rx FIFO threshold */
> > +       .rft            = 8,
> > +       /* std. mode operation */
> > +       .clk_freq       = 100000,
> > +       /* Slave response timeout(ms) */
> > +       .timeout        = 200,
> > +       .sm             = I2C_FREQ_MODE_FAST,
> > +};
>
> So why don't we create proper device tree bindings for the above platform
> data?
>
> For example several driver under
> Documentation/devicetree/bindings/i2c/*
> define the .clk_freq above as "clock-frequency"
>
> samsung-i2c even has this:
> samsung,i2c-sda-delay =<100>;
> samsung,i2c-max-bus-freq =<100000>;
>
> Where i2c-sda-delay corresponds to slsu above.
>
> I suspect .sm can be derived from the frequency so it
> is "FAST" whenever the frequency>  100000.
>
> 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. :)

--
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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