gpiolib: of: support bias pull disable

On top of looking at PULL_UP and PULL_DOWN flags, also look at
PULL_DISABLE and set the appropriate GPIO flag. The GPIO core will then
pass down this to controllers that support it.

Change-Id: I4ea291dbd4165f5744cc0677a7d20dfed3fa1f3b
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/312114
Tested-by: Eric FOURMONT <eric.fourmont-ext@st.com>
Reviewed-by: Eric FOURMONT <eric.fourmont-ext@st.com>
Domain-Review: Eric FOURMONT <eric.fourmont-ext@st.com>

Author: nunojsa

drivers/gpio/gpiolib-of.c

@@ -354,6 +354,9 @@ struct gpio_desc *gpiod_get_from_of_node(const struct device_node *node,
 	if (flags & OF_GPIO_PULL_DOWN)
 		lflags |= GPIO_PULL_DOWN;
 
+	if (flags & OF_GPIO_PULL_DISABLE)
+		lflags |= GPIO_PULL_DISABLE;
+
 	ret = gpiod_configure_flags(desc, propname, lflags, dflags);
 	if (ret < 0) {
 		gpiod_put(desc);
@@ -556,6 +559,8 @@ struct gpio_desc *of_find_gpio(struct device *dev, const char *con_id,
 		*flags |= GPIO_PULL_UP;
 	if (of_flags & OF_GPIO_PULL_DOWN)
 		*flags |= GPIO_PULL_DOWN;
+	if (of_flags & OF_GPIO_PULL_DISABLE)
+		*flags |= GPIO_PULL_DISABLE;
 
 	return desc;
 }
@@ -621,6 +626,8 @@ static struct gpio_desc *of_parse_own_gpio(struct device_node *np,
 		*lflags |= GPIO_PULL_UP;
 	if (xlate_flags & OF_GPIO_PULL_DOWN)
 		*lflags |= GPIO_PULL_DOWN;
+	if (xlate_flags & OF_GPIO_PULL_DISABLE)
+		*lflags |= GPIO_PULL_DISABLE;
 
 	if (of_property_read_bool(np, "input"))
 		*dflags |= GPIOD_IN;

include/linux/of_gpio.h

@@ -29,6 +29,7 @@ enum of_gpio_flags {
 	OF_GPIO_TRANSITORY = 0x8,
 	OF_GPIO_PULL_UP = 0x10,
 	OF_GPIO_PULL_DOWN = 0x20,
+	OF_GPIO_PULL_DISABLE = 0x40,
 };
 
 #ifdef CONFIG_OF_GPIO