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

[Tim Harvey]

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