gpio: mxs: implement get_direction callback

gpiolib's gpiod_get_direction() function returns the EINVAL error
if .get_direction callback is not defined.
The patch implements the callback for mxs chip which is useful
for debugging.

Inspired by arch/arm/mach-at91/gpio.c

On the moment the patch is required to get the patch
"serial: mxs-auart: enable PPS support" working.
It is planned to introduce new mctrl_gpio helpers to avoid
gpiod_get_direction() function.
Signed-off-by: Janusz Uzycki <j.uzycki@elproma.com.pl>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mxs.c

@@ -227,6 +227,18 @@ static int mxs_gpio_to_irq(struct gpio_chip *gc, unsigned offset)
 	return irq_find_mapping(port->domain, offset);
 }
 
+static int mxs_gpio_get_direction(struct gpio_chip *gc, unsigned offset)
+{
+	struct bgpio_chip *bgc = to_bgpio_chip(gc);
+	struct mxs_gpio_port *port =
+		container_of(bgc, struct mxs_gpio_port, bgc);
+	u32 mask = 1 << offset;
+	u32 dir;
+
+	dir = readl(port->base + PINCTRL_DOE(port));
+	return !(dir & mask);
+}
+
 static struct platform_device_id mxs_gpio_ids[] = {
 	{
 		.name = "imx23-gpio",
@@ -320,6 +332,7 @@ static int mxs_gpio_probe(struct platform_device *pdev)
 		goto out_irqdesc_free;
 
 	port->bgc.gc.to_irq = mxs_gpio_to_irq;
+	port->bgc.gc.get_direction = mxs_gpio_get_direction;
 	port->bgc.gc.base = port->id * 32;
 
 	err = gpiochip_add(&port->bgc.gc);