[PATCH] driver: gpio: fix gpio glitch for output-high gpio-hog

[Tim Harvey]

On Wed, Mar 2, 2022 at 6:01 PM Tim Harvey <tharvey at gateworks.com> wrote:
>
> A gpio-hog can be specified as output-low, output-high, or input where
> output-low means 'de-asserted' and 'output-high' means asserted vs
> voltage levels.
>
> When a hog is probed gpio_request_tail() calls dm_gpio_set_dir_flags()
> which ends up setting the GPIO as an output with a driven 'de-asserted'
> value prior to setting the desired value the hog was configured for.
> While I'm not sure it makes sense to set the output level while simply
> 'requesting' a GPIO the result of this is that if the hog is configured
> for output-high the request call sets it first as output low before
> gpio_hog_probe() sets it to the configured value causing the gpio to
> 'glitch' which may be undesired for certain applications.
>
> Fix this by setting the GPIOD_IS_OUT_ACTIVE flag for hogs configured as
> output-high.
>
> This was tested with the following hogs:
>
>         /* active-high output-low (de-asserted) GPIO should drive 0 */
>         gpio1 {
>                 gpio-hog;
>                 output-low;
>                 gpios = <1 GPIO_ACTIVE_HIGH>;
>                 line-name = "gpio1";
>         };
>
>         /* active-high output-high (asserted) GPIO should drive 1 */
>         /* before patch this would first drive 0 then 1 */
>         gpio2 {
>                 gpio-hog;
>                 output-high;
>                 gpios = <2 GPIO_ACTIVE_HIGH>;
>                 line-name = "gpio2";
>         };
>
>         /* active-low output-low (de-asserted) GPIO should drive 1 */
>         gpio3 {
>                 gpio-hog;
>                 output-low;
>                 gpios = <3 GPIO_ACTIVE_LOW>;
>                 line-name = "gpio3#";
>         };
>
>         /* active-low output-high (asserted) GPIO should drive 0 */
>         /* before patch this would first drive 0 then 1 */
>         gpio4 {
>                 gpio-hog;
>                 output-high;
>                 gpios = <4 GPIO_ACTIVE_LOW>;
>                 line-name = "gpio4#";
>         };
>
> Cc: Sean Anderson <sean.anderson at seco.com>
> Signed-off-by: Tim Harvey <tharvey at gateworks.com>
> ---
>  drivers/gpio/gpio-uclass.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpio/gpio-uclass.c b/drivers/gpio/gpio-uclass.c
> index 125ae53d612f..baf9d451c19d 100644
> --- a/drivers/gpio/gpio-uclass.c
> +++ b/drivers/gpio/gpio-uclass.c
> @@ -294,6 +294,8 @@ static int gpio_hog_probe(struct udevice *dev)
>         struct gpio_hog_priv *priv = dev_get_priv(dev);
>         int ret;
>
> +       if (plat->gpiod_flags == GPIOD_IS_OUT && plat->value)
> +               plat->gpiod_flags |= GPIOD_IS_OUT_ACTIVE;
>         ret = gpio_dev_request_index(dev->parent, dev->name, "gpio-hog",
>                                      plat->val[0], plat->gpiod_flags,
>                                      plat->val[1], &priv->gpiod);
> --
> 2.17.1
>

Widening the net here to those who were involved in the gpio-hog support:

Cc: Heiko Schocher <hs at denx.de>
Cc: Michal Simek <michal.simek at xilinx.com>
Cc: Patrick Delaunay <patrick.delaunay at st.com>

Best Regards,

Tim