linux-kernel - Re: [PATCH v3 1/3] gpio: vf610: add support to DT 'ngpios' property

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Date: Thu, 18 Jan 2024 13:44:23 +0100
From: Hector Palacios <hector.palacios@...i.com>
To: Bartosz Golaszewski <brgl@...ev.pl>,
 Andy Shevchenko <andy.shevchenko@...il.com>
Cc: linus.walleij@...aro.org, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, andy@...nel.org, conor+dt@...nel.org,
 shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
 festevam@...il.com, linux-imx@....com, stefan@...er.ch,
 linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] gpio: vf610: add support to DT 'ngpios' property

On 1/18/24 13:03, Bartosz Golaszewski wrote:
> 
> On Thu, Jan 18, 2024 at 10:04 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
>>
>> On Thu, Jan 18, 2024 at 10:25 AM Hector Palacios
>> <hector.palacios@...i.com> wrote:
>>> On 1/17/24 21:51, Andy Shevchenko wrote:
>>>>> Some SoCs, such as i.MX93, don't have all 32 pins available
>>>>> per port. Allow optional generic 'ngpios' property to be
>>>>> specified from the device tree and default to
>>>>> VF610_GPIO_PER_PORT (32) if the property does not exist.
>>
>> ...
>>
>>>>> +       ret = device_property_read_u32(dev, "ngpios", &ngpios);
>>>>> +       if (ret || ngpios > VF610_GPIO_PER_PORT)
>>>>> +               gc->ngpio = VF610_GPIO_PER_PORT;
>>>>> +       else
>>>>> +               gc->ngpio = (u16)ngpios;
>>>>
>>>> This property is being read by the GPIOLIB core. Why do you need to repeat this?
>>>
>>> My apologies; I had not seen this.
>>> I'll use gpiochip_get_ngpios() on the next iteration.
>>
>> But still why?
>> https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib.c#L867
>>
>> It's called for every driver.
>>
>> Maybe it's needed to be refactored to allow fallbacks? Then can the
>> GPIO MMIO case also be updated?
>>
> 
> I guess it's because Hector wants to set an upper limit on the number of GPIOs?

I think Andy is suggesting to rework the gpio-vf610 driver to use 
bgpio_chip struct (it doesn't currently), and then I guess the 'ngpio' 
property gets read automatically if you call bgpio_init().
-- 
Héctor Palacios