linux-kernel - Re: [PATCH 2/5] gpiolib / ACPI: convert to gpiod interfaces

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Date:	Wed, 9 Oct 2013 09:36:50 -0700
From:	Alexandre Courbot <gnurou@...il.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	rjw@...ysocki.net, Linus Walleij <linus.walleij@...aro.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Alexandre Courbot <acourbot@...dia.com>,
	Rob Landley <rob@...dley.net>, linux-acpi@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] gpiolib / ACPI: convert to gpiod interfaces

On Wed, Oct 9, 2013 at 12:58 AM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> On Tue, Oct 08, 2013 at 09:24:50AM -0700, Alexandre Courbot wrote:
>> On Tue, Oct 8, 2013 at 1:45 AM, Mika Westerberg
>> <mika.westerberg@...ux.intel.com> wrote:
>> > On Mon, Oct 07, 2013 at 09:54:13PM -0700, Alexandre Courbot wrote:
>> >> > +struct gpio_desc *acpi_get_gpiod(char *path, int pin)
>> >> >  {
>> >> >         struct gpio_chip *chip;
>> >> >         acpi_handle handle;
>> >> > @@ -48,18 +49,15 @@ int acpi_get_gpio(char *path, int pin)
>> >> >
>> >> >         status = acpi_get_handle(NULL, path, &handle);
>> >> >         if (ACPI_FAILURE(status))
>> >> > -               return -ENODEV;
>> >> > +               return ERR_PTR(-ENODEV);
>> >> >
>> >> >         chip = gpiochip_find(handle, acpi_gpiochip_find);
>> >> >         if (!chip)
>> >> > -               return -ENODEV;
>> >> > +               return ERR_PTR(-ENODEV);
>> >> >
>> >> > -       if (!gpio_is_valid(chip->base + pin))
>> >> > -               return -EINVAL;
>> >> > -
>> >> > -       return chip->base + pin;
>> >> > +       return gpio_to_desc(chip->base + pin);
>> >>
>> >> I think you want to avoid using gpio_to_desc(). It is just a
>> >> convenience function provided to ease the transition for consumers
>> >> that still need to rely on GPIO numbers for some reason. The same
>> >> applies to desc_to_gpio(), although the usage you are making of it
>> >> (implemented fallbacks for the integer space) is the one that is
>> >> intended.
>> >>
>> >> The last line could be changed to "return &chip->desc[pin];" after
>> >> checking that 0 <= pin <= chip->ngpio.
>> >
>> > I tried that but it doesn't compile anymore :-(
>> >
>> > drivers/gpio/gpiolib-acpi.c: In function ‘acpi_get_gpiod’:
>> > drivers/gpio/gpiolib-acpi.c:61:2: error: invalid use of undefined type ‘struct gpio_desc’
>> > drivers/gpio/gpiolib-acpi.c:61:20: error: dereferencing pointer to incomplete type
>>
>> Ah right, there is no way to know the size of a gpio_desc from here...
>> Maybe I should make a gpiochip_get_desc(index) function accessible to
>> drivers only that takes care of this. Another possibility would be to
>> move this function into gpiolib.c but there are probably too many
>> dependencies with ACPI for that.
>>
>> In the long term I would like to see gpio_to_desc()/desc_to_gpio()
>> disappear from the consumer interface as they allow unsafe use of GPIO
>> descriptors.
>>
>> > The DT version also uses gpio_to_desc().
>>
>> That seems to speak in favor of that gpiochip_get_desc() function I
>> talked about earlier.
>
> OK, I can convert the ACPI code to use that once such function exists. I
> the meanwhile, can I use gpio_to_desc() in the next revision of the
> patches?

Sure, please do so - anyway that's the only way you have at the
moment. I will add gpiochip_get_desc() to v2 of gpiod and we'll
convert your code either before or after it is merged, depending on
our timing.
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