linux-kernel - Re: [PATCH] gpiolib: don't clear FLAG_IS_OUT when emulating open-drain/open-source

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Message-ID: <CAMRc=MdtN9E7dP1eSgC52oa7eQ_2HTo6gf9s1cgoxS=j57CK-Q@mail.gmail.com>
Date:   Tue, 17 Sep 2019 09:54:34 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        stable <stable@...r.kernel.org>,
        Kent Gibson <warthog618@...il.com>
Subject: Re: [PATCH] gpiolib: don't clear FLAG_IS_OUT when emulating open-drain/open-source

wt., 10 wrz 2019 o 10:22 Bartosz Golaszewski <brgl@...ev.pl> napisał(a):
>
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>
> When emulating open-drain/open-source by not actively driving the output
> lines - we're simply changing their mode to input. This is wrong as it
> will then make it impossible to change the value of such line - it's now
> considered to actually be in input mode. If we want to still use the
> direction_input() callback for simplicity then we need to set FLAG_IS_OUT
> manually in gpiod_direction_output() and not clear it in
> gpio_set_open_drain_value_commit() and
> gpio_set_open_source_value_commit().
>
> Fixes: c663e5f56737 ("gpio: support native single-ended hardware drivers")
> Cc: stable@...r.kernel.org
> Reported-by: Kent Gibson <warthog618@...il.com>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> ---
>  drivers/gpio/gpiolib.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index cca749010cd0..6bb4191d3844 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2769,8 +2769,10 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
>                 if (!ret)
>                         goto set_output_value;
>                 /* Emulate open drain by not actively driving the line high */
> -               if (value)
> -                       return gpiod_direction_input(desc);
> +               if (value) {
> +                       ret = gpiod_direction_input(desc);
> +                       goto set_output_flag;
> +               }
>         }
>         else if (test_bit(FLAG_OPEN_SOURCE, &desc->flags)) {
>                 ret = gpio_set_config(gc, gpio_chip_hwgpio(desc),
> @@ -2778,8 +2780,10 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
>                 if (!ret)
>                         goto set_output_value;
>                 /* Emulate open source by not actively driving the line low */
> -               if (!value)
> -                       return gpiod_direction_input(desc);
> +               if (!value) {
> +                       ret = gpiod_direction_input(desc);
> +                       goto set_output_flag;
> +               }
>         } else {
>                 gpio_set_config(gc, gpio_chip_hwgpio(desc),
>                                 PIN_CONFIG_DRIVE_PUSH_PULL);
> @@ -2787,6 +2791,17 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
>
>  set_output_value:
>         return gpiod_direction_output_raw_commit(desc, value);
> +
> +set_output_flag:
> +       /*
> +        * When emulating open-source or open-drain functionalities by not
> +        * actively driving the line (setting mode to input) we still need to
> +        * set the IS_OUT flag or otherwise we won't be able to set the line
> +        * value anymore.
> +        */
> +       if (ret == 0)
> +               set_bit(FLAG_IS_OUT, &desc->flags);
> +       return ret;
>  }
>  EXPORT_SYMBOL_GPL(gpiod_direction_output);
>
> @@ -3147,8 +3162,6 @@ static void gpio_set_open_drain_value_commit(struct gpio_desc *desc, bool value)
>
>         if (value) {
>                 err = chip->direction_input(chip, offset);
> -               if (!err)
> -                       clear_bit(FLAG_IS_OUT, &desc->flags);
>         } else {
>                 err = chip->direction_output(chip, offset, 0);
>                 if (!err)
> @@ -3178,8 +3191,6 @@ static void gpio_set_open_source_value_commit(struct gpio_desc *desc, bool value
>                         set_bit(FLAG_IS_OUT, &desc->flags);
>         } else {
>                 err = chip->direction_input(chip, offset);
> -               if (!err)
> -                       clear_bit(FLAG_IS_OUT, &desc->flags);
>         }
>         trace_gpio_direction(desc_to_gpio(desc), !value, err);
>         if (err < 0)
> --
> 2.21.0
>

Queued for fixes.

Bart