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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Tue, 15 Dec 2020 18:42:36 +0100
Message-ID: <CAMpxmJU0XWxiYr716MNGnORJJJ-czuBGWNnFTa5oBTUK4uVheQ@mail.gmail.com>
Subject: Re: [PATCH] gpiolib: Allow name duplicates of "" and "NC"
To:     Bjorn Andersson <bjorn.andersson@linaro.org>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        linux-gpio <linux-gpio@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arm-msm@vger.kernel.org
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On Tue, Dec 15, 2020 at 6:02 PM Bjorn Andersson
<bjorn.andersson@linaro.org> wrote:
>
> Not all GPIO pins are exposed to the world and this is typically
> described by not giving these lines particular names, commonly "" or
> "NC".
>
> With the recent introduction of '2cd64ae98f35 ("gpiolib: Disallow
> identical line names in the same chip")' any gpiochip with multiple such
> pins will refuse to probe.
>
> Fix this by treating "" and "NC" as "no name specified" in
> gpio_name_to_desc()
>
> Fixes: 2cd64ae98f35 ("gpiolib: Disallow identical line names in the same chip")
> Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> ---
>
> The introduction of 2cd64ae98f35 breaks pretty much all Qualcomm boards and
> grepping the DT tree indicates that other vendors will have the same problem.
>
> In addition to this the am335x-* boards will also needs "[NC]", "[ethernet]",
> "[emmc"], "[i2c0]", "[SYSBOOT]" and "[JTAG]" added to this list to allow
> booting v5.11 with the past and present dtb/dts files.
>
>  drivers/gpio/gpiolib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index b3340ba68471..407ba79ae571 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -302,7 +302,7 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
>         struct gpio_device *gdev;
>         unsigned long flags;
>
> -       if (!name)
> +       if (!name || !strcmp(name, "") || !strcmp(name, "NC"))
>                 return NULL;
>
>         spin_lock_irqsave(&gpio_lock, flags);
> --
> 2.29.2
>

I have a bad feeling about this. This opens the door for all kinds of
exceptions: "N/A", "none" etc. Depending on whose boards are getting
broken.

If non-uniqueness of names is needed then let's better revert 2cd64ae98f35.

Bartosz