Re: [PATCH v2 5/6] gpiolib: disable bias on inputs when pull up/down are both set

[Bartosz Golaszewski <brgl@xxxxxxxx>]

sob., 12 paź 2019 o 03:57 Kent Gibson <warthog618@xxxxxxxxx> napisał(a):
>
> This patch allows pull up/down bias to be disabled, allowing
> the line to float or to be biased only by external circuitry.
> Use case is for where the bias has been applied previously,
> either by default or by the user, but that setting may
> conflict with the current use of the line.
>
> Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
> ---
>  drivers/gpio/gpiolib.c | 22 +++++++---------------
>  1 file changed, 7 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 647334f53622..f90b20d548b9 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -539,11 +539,6 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
>             (lflags & GPIOHANDLE_REQUEST_OUTPUT))
>                 return -EINVAL;
>
> -       /* Same with pull-up and pull-down. */
> -       if ((lflags & GPIOHANDLE_REQUEST_PULL_UP) &&
> -           (lflags & GPIOHANDLE_REQUEST_PULL_DOWN))
> -               return -EINVAL;
> -
>         /*
>          * Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
>          * the hardware actually supports enabling both at the same time the
> @@ -935,14 +930,6 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
>              (lflags & GPIOHANDLE_REQUEST_PULL_DOWN)))
>                 return -EINVAL;
>
> -       /*
> -        * Do not allow both pull-up and pull-down flags to be set as they
> -        *  are contradictory.
> -        */
> -       if ((lflags & GPIOHANDLE_REQUEST_PULL_UP) &&
> -           (lflags & GPIOHANDLE_REQUEST_PULL_DOWN))
> -               return -EINVAL;
> -
>         le = kzalloc(sizeof(*le), GFP_KERNEL);
>         if (!le)
>                 return -ENOMEM;
> @@ -2931,6 +2918,7 @@ static int gpio_set_config(struct gpio_chip *gc, unsigned offset,
>         unsigned arg;
>
>         switch (mode) {
> +       case PIN_CONFIG_BIAS_DISABLE:
>         case PIN_CONFIG_BIAS_PULL_DOWN:
>         case PIN_CONFIG_BIAS_PULL_UP:
>                 arg = 1;
> @@ -2991,7 +2979,11 @@ int gpiod_direction_input(struct gpio_desc *desc)
>         if (ret == 0)
>                 clear_bit(FLAG_IS_OUT, &desc->flags);
>
> -       if (test_bit(FLAG_PULL_UP, &desc->flags))
> +       if (test_bit(FLAG_PULL_UP, &desc->flags) &&
> +               test_bit(FLAG_PULL_DOWN, &desc->flags))
> +               gpio_set_config(chip, gpio_chip_hwgpio(desc),
> +                               PIN_CONFIG_BIAS_DISABLE);
> +       else if (test_bit(FLAG_PULL_UP, &desc->flags))

>From looking at the code: user-space can disable bias when setting
both PULL_UP and PULL_DOWN flags. I don't understand why it's done in
this implicit way? Why not a separate flag? Also: I don't like that
this patch deletes code added by earlier patches in this series. If we
really need this, then it should be rearranged.

Bart

>                 gpio_set_config(chip, gpio_chip_hwgpio(desc),
>                                 PIN_CONFIG_BIAS_PULL_UP);
>         else if (test_bit(FLAG_PULL_DOWN, &desc->flags))
> @@ -4462,7 +4454,7 @@ int gpiod_configure_flags(struct gpio_desc *desc, const char *con_id,
>
>         if (lflags & GPIO_PULL_UP)
>                 set_bit(FLAG_PULL_UP, &desc->flags);
> -       else if (lflags & GPIO_PULL_DOWN)
> +       if (lflags & GPIO_PULL_DOWN)
>                 set_bit(FLAG_PULL_DOWN, &desc->flags);
>
>         ret = gpiod_set_transitory(desc, (lflags & GPIO_TRANSITORY));
> --
> 2.23.0
>