dm: gpio: Add methods for open drain setting

Certain GPIO devices have the capability to switch their GPIOs into
open-drain mode, that is, instead of actively driving the output
(Push-pull output), the pin is connected to the collector (for a NPN
transistor) or the drain (for a MOSFET) of a transistor, respectively.
The pin then either forms an open circuit or a connection to ground,
depending on the state of the transistor.

This patch adds functions to the GPIO uclass to switch GPIOs to
open-drain mode on devices that support it.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: York Sun <york.sun@nxp.com>

drivers/gpio/gpio-uclass.c

@@ -367,6 +367,38 @@ int dm_gpio_set_value(const struct gpio_desc *desc, int value)
 	return 0;
 }
 
+int dm_gpio_get_open_drain(struct gpio_desc *desc)
+{
+	struct dm_gpio_ops *ops = gpio_get_ops(desc->dev);
+	int ret;
+
+	ret = check_reserved(desc, "get_open_drain");
+	if (ret)
+		return ret;
+
+	if (ops->set_open_drain)
+		return ops->get_open_drain(desc->dev, desc->offset);
+	else
+		return -ENOSYS;
+}
+
+int dm_gpio_set_open_drain(struct gpio_desc *desc, int value)
+{
+	struct dm_gpio_ops *ops = gpio_get_ops(desc->dev);
+	int ret;
+
+	ret = check_reserved(desc, "set_open_drain");
+	if (ret)
+		return ret;
+
+	if (ops->set_open_drain)
+		ret = ops->set_open_drain(desc->dev, desc->offset, value);
+	else
+		return 0; /* feature not supported -> ignore setting */
+
+	return ret;
+}
+
 int dm_gpio_set_dir_flags(struct gpio_desc *desc, ulong flags)
 {
 	struct udevice *dev = desc->dev;

include/asm-generic/gpio.h

@@ -251,6 +251,8 @@ struct dm_gpio_ops {
 				int value);
 	int (*get_value)(struct udevice *dev, unsigned offset);
 	int (*set_value)(struct udevice *dev, unsigned offset, int value);
+	int (*get_open_drain)(struct udevice *dev, unsigned offset);
+	int (*set_open_drain)(struct udevice *dev, unsigned offset, int value);
 	/**
 	 * get_function() Get the GPIO function
 	 *
@@ -550,6 +552,38 @@ int dm_gpio_get_value(const struct gpio_desc *desc);
 int dm_gpio_set_value(const struct gpio_desc *desc, int value);
 
 /**
+ * dm_gpio_get_open_drain() - Check if open-drain-mode of a GPIO is active
+ *
+ * This checks if open-drain-mode for a GPIO is enabled or not. This method is
+ * optional.
+ *
+ * @desc:	GPIO description containing device, offset and flags,
+ *		previously returned by gpio_request_by_name()
+ * @return Value of open drain mode for GPIO (0 for inactive, 1 for active) or
+ *	   -ve on error
+ */
+int dm_gpio_get_open_drain(struct gpio_desc *desc);
+
+/**
+ * dm_gpio_set_open_drain() - Switch open-drain-mode of a GPIO on or off
+ *
+ * This enables or disables open-drain mode for a GPIO. This method is
+ * optional; if the driver does not support it, nothing happens when the method
+ * is called.
+ *
+ * In open-drain mode, instead of actively driving the output (Push-pull
+ * output), the GPIO's pin is connected to the collector (for a NPN transistor)
+ * or the drain (for a MOSFET) of a transistor, respectively. The pin then
+ * either forms an open circuit or a connection to ground, depending on the
+ * state of the transistor.
+ *
+ * @desc:	GPIO description containing device, offset and flags,
+ *		previously returned by gpio_request_by_name()
+ * @return 0 if OK, -ve on error
+ */
+int dm_gpio_set_open_drain(struct gpio_desc *desc, int value);
+
+/**
  * dm_gpio_set_dir() - Set the direction for a GPIO
  *
  * This sets up the direction according tot the provided flags. It will do