linux-kernel - Re: [PATCH] gpiolib: fix efficiency regression when using gpio_chip_get

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Message-ID: <CAMRc=MdP5BMVF0p5W9qSRZuPKBa0YCTxB-gLQWT_r0hBp+8ksA@mail.gmail.com>
Date: Fri, 4 Jul 2025 10:26:58 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Hugo Villeneuve <hugo@...ovil.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Hugo Villeneuve <hvilleneuve@...onoff.com>, 
	stable@...r.kernel.org, Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpiolib: fix efficiency regression when using gpio_chip_get_multiple()

On Thu, Jul 3, 2025 at 9:18 PM Hugo Villeneuve <hugo@...ovil.com> wrote:
>
> From: Hugo Villeneuve <hvilleneuve@...onoff.com>
>
> commit 74abd086d2ee ("gpiolib: sanitize the return value of
> gpio_chip::get_multiple()") altered the value returned by
> gc->get_multiple() in case it is positive (> 0), but failed to
> return for other cases (<= 0).
>
> This may result in the "if (gc->get)" block being executed and thus
> negates the performance gain that is normally obtained by using
> gc->get_multiple().
>
> Fix by returning the result of gc->get_multiple() if it is <= 0.
>
> Also move the "ret" variable to the scope where it is used, which as an
> added bonus fixes an indentation error introduced by the aforementioned
> commit.

Thanks, I queued it for fixes. I typically keep local variables at the
top of the function (just a personal readability preference) but since
this function already has scope-local variables, let's do it. What is
the indentation error you're mentioning exactly?

Bart

>
> Fixes: 74abd086d2ee ("gpiolib: sanitize the return value of gpio_chip::get_multiple()")
> Cc: stable@...r.kernel.org
> Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> ---
>  drivers/gpio/gpiolib.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index fdafa0df1b43..3a3eca5b4c40 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -3297,14 +3297,15 @@ static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
>  static int gpio_chip_get_multiple(struct gpio_chip *gc,
>                                   unsigned long *mask, unsigned long *bits)
>  {
> -       int ret;
> -
>         lockdep_assert_held(&gc->gpiodev->srcu);
>
>         if (gc->get_multiple) {
> +               int ret;
> +
>                 ret = gc->get_multiple(gc, mask, bits);
>                 if (ret > 0)
>                         return -EBADE;
> +               return ret;
>         }
>
>         if (gc->get) {
>
> base-commit: b4911fb0b060899e4eebca0151eb56deb86921ec
> --
> 2.39.5
>