linux-kernel - Re: [PATCH v3] gpio: add GPIO support for F71882FG and F71889F

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Date:	Mon, 29 Jul 2013 17:59:08 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Simon Guinot <simon.guinot@...uanux.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v3] gpio: add GPIO support for F71882FG and F71889F

On Mon, Jul 22, 2013 at 11:50 AM, Simon Guinot
<simon.guinot@...uanux.org> wrote:

> This patch adds support for the GPIOs found on the Fintek super-I/O
> chips F71882FG and F71889F.
>
> A super-I/O is a legacy I/O controller embedded on x86 motherboards. It
> is used to connect the low-bandwidth devices. Among others functions the
> F71882FG/F71889F provides: a parallel port, two serial ports, a keyboard
> controller, an hardware monitoring controller and some GPIO pins.
>
> Note that this super-I/Os are embedded on some Atom-based LaCie NASes.
> The GPIOs are used to control the LEDs and the hard drive power.
>
> Signed-off-by: Simon Guinot <simon.guinot@...uanux.org>
> ---
> Changes since v2:
> - Remove useless NULL setters for driver data.

Given the recent discussion with Rafael I want to have an
extended discussion of this patch.

It is my current understanding that:

- It is possible to define the whereabouts of the SuperIO
  chips using ACPI
- It is possible for developers to influence the source
  AML for the DSDT tables of these systems.
- It is the proper thing to do.
- So we should atleast support ACPI probing with the
  port-based detection as a final fallback if all else fails.

Why can I not get something like:

#include <linux/acpi.h>
(...)
static const struct acpi_device_id gpio_acpi_match[] = {
        { "FOOBAR", 0 },
        { }
};
MODULE_DEVICE_TABLE(acpi, gpio_acpi_match);

static struct platform_driver gpio_driver = {
        (...)
        .driver         = {
                 (...)
                .acpi_match_table = ACPI_PTR(gpio_acpi_match),
        },
};

?

If there is something wrong in my reasoning above, please
share it!

Yours,
Linus Walleij
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