Re: [RFC] gpio: expose pull-up/pull-down line flags to userspace

[Bartosz Golaszewski <brgl@xxxxxxxx>]

sob., 21 wrz 2019 o 12:27 Drew Fustini <drew@xxxxxxxx> napisał(a):
>
> Add pull-up/pull-down flags to the gpio line get and
> set ioctl() calls.  Use cases include a push button
> that does not have an external resistor.
>
> Addition use cases described by Limor Fried (ladyada) of
> Adafruit in this PR for Adafruit_Blinka Python lib:
> https://github.com/adafruit/Adafruit_Blinka/pull/59
>
> Signed-off-by: Drew Fustini <drew@xxxxxxxx>
> ---
>  drivers/gpio/gpiolib.c    | 12 ++++++++++++
>  include/uapi/linux/gpio.h |  4 ++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index d9074191edef..9da1093cc7f5 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -427,6 +427,8 @@ struct linehandle_state {
>         (GPIOHANDLE_REQUEST_INPUT | \
>         GPIOHANDLE_REQUEST_OUTPUT | \
>         GPIOHANDLE_REQUEST_ACTIVE_LOW | \
> +       GPIOHANDLE_REQUEST_PULL_UP | \
> +       GPIOHANDLE_REQUEST_PULL_DOWN | \
>         GPIOHANDLE_REQUEST_OPEN_DRAIN | \
>         GPIOHANDLE_REQUEST_OPEN_SOURCE)
>
> @@ -598,6 +600,10 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
>                         set_bit(FLAG_OPEN_DRAIN, &desc->flags);
>                 if (lflags & GPIOHANDLE_REQUEST_OPEN_SOURCE)
>                         set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> +               if (lflags & GPIOHANDLE_REQUEST_PULL_DOWN)
> +                       set_bit(FLAG_PULL_DOWN, &desc->flags);
> +               if (lflags & GPIOHANDLE_REQUEST_PULL_UP)
> +                       set_bit(FLAG_PULL_UP, &desc->flags);
>
>                 ret = gpiod_set_transitory(desc, false);
>                 if (ret < 0)
> @@ -1102,6 +1108,10 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>                 if (test_bit(FLAG_OPEN_SOURCE, &desc->flags))
>                         lineinfo.flags |= (GPIOLINE_FLAG_OPEN_SOURCE |
>                                            GPIOLINE_FLAG_IS_OUT);
> +               if (test_bit(FLAG_PULL_DOWN, &desc->flags))
> +                       lineinfo.flags |= GPIOLINE_FLAG_PULL_DOWN;
> +               if (test_bit(FLAG_PULL_UP, &desc->flags))
> +                       lineinfo.flags |= GPIOLINE_FLAG_PULL_UP;
>
>                 if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
>                         return -EFAULT;
> @@ -2475,6 +2485,8 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
>                 clear_bit(FLAG_REQUESTED, &desc->flags);
>                 clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
>                 clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
> +               clear_bit(FLAG_PULL_UP, &desc->flags);
> +               clear_bit(FLAG_PULL_DOWN, &desc->flags);
>                 clear_bit(FLAG_IS_HOGGED, &desc->flags);
>                 ret = true;
>         }
> diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
> index 4ebfe0ac6c5b..c2d1f7d908d6 100644
> --- a/include/uapi/linux/gpio.h
> +++ b/include/uapi/linux/gpio.h
> @@ -33,6 +33,8 @@ struct gpiochip_info {
>  #define GPIOLINE_FLAG_ACTIVE_LOW       (1UL << 2)
>  #define GPIOLINE_FLAG_OPEN_DRAIN       (1UL << 3)
>  #define GPIOLINE_FLAG_OPEN_SOURCE      (1UL << 4)
> +#define GPIOLINE_FLAG_PULL_UP  (1UL << 5)
> +#define GPIOLINE_FLAG_PULL_DOWN        (1UL << 6)
>
>  /**
>   * struct gpioline_info - Information about a certain GPIO line
> @@ -62,6 +64,8 @@ struct gpioline_info {
>  #define GPIOHANDLE_REQUEST_ACTIVE_LOW  (1UL << 2)
>  #define GPIOHANDLE_REQUEST_OPEN_DRAIN  (1UL << 3)
>  #define GPIOHANDLE_REQUEST_OPEN_SOURCE (1UL << 4)
> +#define GPIOHANDLE_REQUEST_PULL_UP     (1UL << 5)
> +#define GPIOHANDLE_REQUEST_PULL_DOWN   (1UL << 6)
>
>  /**
>   * struct gpiohandle_request - Information about a GPIO handle request
> --
> 2.20.1
>

Hi Drew,

I remember discussing it with Linus some time ago. This may not be as
straightforward as simply adding new flags. Since PULL-UP/DOWN
resistors can - among other parameters - also have configurable
resistance, we'll probably need some kind of a structure for this
ioctl() to pass any additional information to the kernel. Since we
can't change ABI this may require adding a whole new ioctl() for
extended configuration. This in turn has to be as future-proof as
possible - if someone asks for user-space-configurable drive-strength,
the new ioctl() should be ready for it.

I should have some bandwidth in the coming days, so I'll try to give it a try.

Bart