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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Tue, 12 May 2020 12:43:16 +0200
Message-ID: <CAMpxmJXD9WgrFnKvS2a=iOCVuYiqdTGwp+r2BjOv2RJH2R=s1Q@mail.gmail.com>
Subject: Re: [PATCH] gpiolib: Document that GPIO line names are not globally unique
To:     Geert Uytterhoeven <geert+renesas@glider.be>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        linux-gpio <linux-gpio@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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pon., 11 maj 2020 o 12:18 Geert Uytterhoeven <geert+renesas@glider.be>
napisa=C5=82(a):
>
> gpiochip_set_desc_names() no longer rejects GPIO line name collisions.
> Hence GPIO line names are not guaranteed to be globally unique.
> In case of multiple GPIO lines with the same name, gpio_name_to_desc()
> will return the first match found.
>
> Update the comments for gpio_name_to_desc() and
> gpiochip_set_desc_names() to match reality.
>
> Fixes: f881bab038c9667d ("gpio: keep the GPIO line names internal")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
>  drivers/gpio/gpiolib.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 99533f4cb5d332a9..98822412f565073a 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -296,6 +296,9 @@ static int gpiodev_add_to_list(struct gpio_device *gd=
ev)
>
>  /*
>   * Convert a GPIO name to its descriptor
> + * Note that there is no guarantee that GPIO names are globally unique!
> + * Hence this function will return, if it exists, a reference to the fir=
st GPIO
> + * line found that matches the given name.
>   */
>  static struct gpio_desc *gpio_name_to_desc(const char * const name)
>  {
> @@ -329,10 +332,12 @@ static struct gpio_desc *gpio_name_to_desc(const ch=
ar * const name)
>  }
>
>  /*
> - * Takes the names from gc->names and checks if they are all unique. If =
they
> - * are, they are assigned to their gpio descriptors.
> + * Take the names from gc->names and assign them to their GPIO descripto=
rs.
> + * Warn if a name is already used for a GPIO line on a different GPIO ch=
ip.
>   *
> - * Warning if one of the names is already used for a different GPIO.
> + * Note that:
> + *   1. Non-unique names are still accepted,
> + *   2. Name collisions within the same GPIO chip are not reported.
>   */
>  static int gpiochip_set_desc_names(struct gpio_chip *gc)
>  {
> --
> 2.17.1
>

This makes me wonder whether I should do something about this in
libgpiod? Looks to me like gpiod_chip_find_line() and the global
gpiod_line_find() are no longer reliable and should probably return
all lines whose names match.

Bart