[PATCH 3/4] gpiolib: Add support for GPIO "hog" nodes

[Andrey Smirnov]

On Mon, May 22, 2017 at 11:52 PM, Nikita Yushchenko
<nikita.yoush at cogentembedded.com> wrote:
>> +     ret = of_property_read_u32(chip_np, "#gpio-cells", &gpio_cells);
>> +     if (ret)
>> +             return ret;
>> +
>> +     if (WARN_ON(gpio_cells != 2))
>> +             return -ENOTSUPP;
>> +
>> +     ret = of_property_read_u32_index(np, "gpios", idx * gpio_cells,
>> +                                      &gpio_num);
>> +     if (ret)
>> +             return ret;
>> +
>> +     ret = of_property_read_u32_index(np, "gpios", idx * gpio_cells + 1,
>> +                                      &gpio_flags);
>> +     if (ret)
>> +             return ret;
>
> Doesn't this hardcode interpretation of device tree words in gpio
> specification - while this is intended to be gpio-provider specific and
> that's why #gpio-cells exist?
>

It does and yes that's my understanding of the purpose of #gpio-cells
as well. The reason I did in such a primitive way was because
Barebox's GPIO subsystem doesn't have any translation plumbing to be
able to handle anything more than a simple one dimensional offset.
Given the fact that of_get_named_gpio_flags() make similar assumption
I thought that there are no real consumers of that functionality and
left proper implementation as a future improvement that can be made
once the need arises.

>
>> +static int of_gpiochip_scan_gpios(struct gpio_chip *chip)
>
> Not best choice of name for routine that scans hogs?
>
> (although I understand that it comes from linux counterpart)
>

Eh, I don't have any strong opinion on this one, I am more than happy
to rename it if you think there are better alternatives.

>> -     return 0;
>> +     return of_gpiochip_scan_gpios(chip);
>
> Should we fail gpiochip registration on failure to claim hogs?
> I don't know.

I couldn't think of a use-case where it wasn't basically all or
nothing: either I get everything working or I need to go back and fix
my DT. Sascha, do you have an opinion on this one?

Thanks,
Andrey Smirnov