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

On Wed, Mar 2, 2022 at 6:01 PM Tim Harvey tharvey@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@seco.com Signed-off-by: Tim Harvey tharvey@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@denx.de Cc: Michal Simek michal.simek@xilinx.com Cc: Patrick Delaunay patrick.delaunay@st.com

Best Regards,

Tim