Re: [PATCH V5 2/3] Documentation: gpio: Add APM X-Gene SoC GPIO controller DTS binding

[Feng Kan <fkan@xxxxxxx>]

On Fri, Jul 4, 2014 at 2:28 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> On Mon, Jun 30, 2014 at 2:53 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
>> On Thu, Jun 26, 2014 at 11:59:46PM +0100, Feng Kan wrote:
>
>>> +- #gpio-cells: Should be two.
>>> +     - first cell is the pin number
>>> +     - second cell is used to specify optional parameters (unused)
>>
>> Why is there an unused cell?
>>
>> Why not just make this a single cell if the binding defines no valid
>> parameters?
>
> I don't get this either. The only reason would be that this cell
> should contain flags (such as open collector) the code for using
> it being inplemented later.

Yes, open drain configuration and mux via pinctrl was something I
planned for later.
There was another reason for this as well, part of the gpio code I read
was confusing me. So I look through the other gpio documentations and
found an example that did this as well.

int of_gpio_simple_xlate(struct gpio_chip *gc,
                         const struct of_phandle_args *gpiospec, u32 *flags)
{
        /*
         * We're discouraging gpio_cells < 2, since that way you'll have to
         * write your own xlate function (that will have to retrive the GPIO
         * number and the flags from a single gpio cell -- this is possible,
         * but not recommended).
         */

Thanks, and please advise me on what to do next.
>
> If the controller is too primitive to use such flags it should be onecell.
>
> Yours,
> Linus Walleij
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