iio: resolver: ad2s1210: add reset gpio support

This adds support for the optional reset gpio to the ad2s1210 resolver
driver. If the gpio is present in the device tree, it is toggled during
driver probe before the reset of the device initialization. As per the
devicetree bindings, it is expected for the gpio to configured as active
low.
Suggested-by: Michael Hennerich <Michael.Hennerich@analog.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Link: https://lore.kernel.org/r/20231016154311.38547-1-dlechner@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/resolver/ad2s1210.c

@@ -1426,6 +1426,7 @@ static int ad2s1210_setup_gpios(struct ad2s1210_state *st)
 {
 	struct device *dev = &st->sdev->dev;
 	struct gpio_descs *resolution_gpios;
+	struct gpio_desc *reset_gpio;
 	DECLARE_BITMAP(bitmap, 2);
 	int ret;
 
@@ -1481,6 +1482,17 @@ static int ad2s1210_setup_gpios(struct ad2s1210_state *st)
 					     "failed to set resolution gpios\n");
 	}
 
+	/* If the optional reset GPIO is present, toggle it to do a hard reset. */
+	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(reset_gpio))
+		return dev_err_probe(dev, PTR_ERR(reset_gpio),
+				     "failed to request reset GPIO\n");
+
+	if (reset_gpio) {
+		udelay(10);
+		gpiod_set_value(reset_gpio, 0);
+	}
+
 	return 0;
 }