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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 17 Mar 2020 12:32:31 +0100
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Subject: Re: [PATCH v5 3/5] gpio: Add GPIO Aggregator
To:     Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Harish Jenny K N <harish_kandiga@mentor.com>,
        Eugeniu Rosca <erosca@de.adit-jv.com>,
        Alexander Graf <graf@amazon.com>,
        Peter Maydell <peter.maydell@linaro.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Phil Reid <preid@electromag.com.au>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Christoffer Dall <christoffer.dall@arm.com>,
        Magnus Damm <magnus.damm@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
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On Tue, Feb 18, 2020 at 4:18 PM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
> GPIO controllers are exported to userspace using /dev/gpiochip*
> character devices.  Access control to these devices is provided by
> standard UNIX file system permissions, on an all-or-nothing basis:
> either a GPIO controller is accessible for a user, or it is not.
> Currently no mechanism exists to control access to individual GPIOs.
>
> Hence add a GPIO driver to aggregate existing GPIOs, and expose them as
> a new gpiochip.
>
> This supports the following use cases:
>   - Aggregating GPIOs using Sysfs
>     This is useful for implementing access control, and assigning a set
>     of GPIOs to a specific user or virtual machine.
>   - Generic GPIO Driver
>     This is useful for industrial control, where it can provide
>     userspace access to a simple GPIO-operated device described in DT,
>     cfr. e.g. spidev for SPI-operated devices.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

> --- /dev/null
> +++ b/drivers/gpio/gpio-aggregator.c

> +static int gpio_fwd_set_config(struct gpio_chip *chip, unsigned int offset,
> +                              unsigned long config)
> +{
> +       struct gpiochip_fwd *fwd = gpiochip_get_data(chip);
> +
> +       chip = fwd->descs[offset]->gdev->chip;
> +       if (chip->set_config)

-       chip = fwd->descs[offset]->gdev->chip;
-       if (chip->set_config)
+       chip = gpiod_to_chip(fwd->descs[offset]);
+       if (chip && chip->set_config)

> +               return chip->set_config(chip, offset, config);

This is not correct: offset should be translated, too, i.e.

    offset = gpio_chip_hwgpio(fwd->descs[offset]);

Which adds a new dependency on "gpiolib.h"...

Is there a better alternative, than providing a public gpiod_set_config()
helper?
Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds