spi: sc18is602: Add reset control via gpio pin.

This sc18is602 has a reset pin that may need to be deasserted.
Add optional binding to specifiy the reset pin via a gpio and deassert
during probe.
Signed-off-by: NPhil Reid <preid@electromag.com.au>
Signed-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/spi-sc18is602.c

@@ -23,6 +23,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/of.h>
 #include <linux/platform_data/sc18is602.h>
+#include <linux/gpio/consumer.h>
 
 enum chips { sc18is602, sc18is602b, sc18is603 };
 
@@ -50,6 +51,8 @@ struct sc18is602 {
 	u8			buffer[SC18IS602_BUFSIZ + 1];
 	int			tlen;	/* Data queued for tx in buffer */
 	int			rindex;	/* Receive data index in buffer */
+
+	struct gpio_desc	*reset;
 };
 
 static int sc18is602_wait_ready(struct sc18is602 *hw, int len)
@@ -257,6 +260,12 @@ static int sc18is602_probe(struct i2c_client *client,
 	hw = spi_master_get_devdata(master);
 	i2c_set_clientdata(client, hw);
 
+	/* assert reset and then release */
+	hw->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(hw->reset))
+		return PTR_ERR(hw->reset);
+	gpiod_set_value(hw->reset, 0);
+
 	hw->master = master;
 	hw->client = client;
 	hw->dev = dev;