gpio: vx855: use the new open drain callback

The vx855 driver clearly states it has three groups of lines:
GPI, GPO and GPIO. The GPO are assumedly push-pull. The GPIO
are implicit open drain, but if the GPIO subsystem ask for them
to be explicitly open drain (i.e. set the flag on a machine table
that we want open drain) it will currently misbehave: it will
switch the GPIOs to input mode (emulate open drain). Instead:
indicate in the .set_single_ended() callback that we support
open drain and open drain only.

Cc: Daniel Drake <drake@endlessm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-vx855.c

@@ -186,6 +186,28 @@ static int vx855gpio_direction_output(struct gpio_chip *gpio,
 	return 0;
 }
 
+static int vx855gpio_set_single_ended(struct gpio_chip *gpio,
+				      unsigned int nr,
+				      enum single_ended_mode mode)
+{
+	/* The GPI cannot be single-ended */
+	if (nr < NR_VX855_GPI)
+		return -EINVAL;
+
+	/* The GPO's are push-pull */
+	if (nr < NR_VX855_GPInO) {
+		if (mode != LINE_MODE_PUSH_PULL)
+			return -ENOTSUPP;
+		return 0;
+	}
+
+	/* The GPIO's are open drain */
+	if (mode != LINE_MODE_OPEN_DRAIN)
+		return -ENOTSUPP;
+
+	return 0;
+}
+
 static const char *vx855gpio_names[NR_VX855_GP] = {
 	"VX855_GPI0", "VX855_GPI1", "VX855_GPI2", "VX855_GPI3", "VX855_GPI4",
 	"VX855_GPI5", "VX855_GPI6", "VX855_GPI7", "VX855_GPI8", "VX855_GPI9",
@@ -209,6 +231,7 @@ static void vx855gpio_gpio_setup(struct vx855_gpio *vg)
 	c->direction_output = vx855gpio_direction_output;
 	c->get = vx855gpio_get;
 	c->set = vx855gpio_set;
+	c->set_single_ended = vx855gpio_set_single_ended;
 	c->dbg_show = NULL;
 	c->base = 0;
 	c->ngpio = NR_VX855_GP;