gnss: ubx: add support for the reset gpio

The Renesas KingFisher board includes a U-Blox Neo-M8 chip. This chip
has a reset pin which is also wired on the board. When Linux starts,
reset is asserted by the firmware. Deassert the reset pin when probing
this driver.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
[ johan: rename gpio descriptor variable ]
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/gnss/ubx.c

@@ -7,6 +7,7 @@
 
 #include <linux/errno.h>
 #include <linux/gnss.h>
+#include <linux/gpio/consumer.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -65,6 +66,7 @@ static const struct gnss_serial_ops ubx_gserial_ops = {
 static int ubx_probe(struct serdev_device *serdev)
 {
 	struct gnss_serial *gserial;
+	struct gpio_desc *reset;
 	struct ubx_data *data;
 	int ret;
 
@@ -90,6 +92,13 @@ static int ubx_probe(struct serdev_device *serdev)
 	if (ret < 0 && ret != -ENODEV)
 		goto err_free_gserial;
 
+	/* Deassert reset */
+	reset = devm_gpiod_get_optional(&serdev->dev, "reset", GPIOD_OUT_LOW);
+	if (IS_ERR(reset)) {
+		ret = PTR_ERR(reset);
+		goto err_free_gserial;
+	}
+
 	ret = gnss_serial_register(gserial);
 	if (ret)
 		goto err_free_gserial;