ASoC: ak4104: add reset line property to DT bindings

This device doesn't have a pdata definition for legacy boards, and
unless anyone need to control the reset GPIO, it's not worth adding one.
So this feature is only available to DT users for now.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

Documentation/devicetree/bindings/sound/ak4104.txt

@@ -8,6 +8,11 @@ Required properties:
 
   - reg : The chip select number on the SPI bus
 
+Optional properties:
+
+  - reset-gpio : a GPIO spec for the reset pin. If specified, it will be
+		 deasserted before communication to the device starts.
+
 Example:
 
 spdif: ak4104@0 {

sound/soc/codecs/ak4104.c

@@ -15,6 +15,8 @@
 #include <sound/soc.h>
 #include <sound/initval.h>
 #include <linux/spi/spi.h>
+#include <linux/of_device.h>
+#include <linux/of_gpio.h>
 #include <sound/asoundef.h>
 
 /* AK4104 registers addresses */
@@ -204,6 +206,7 @@ static const struct regmap_config ak4104_regmap = {
 
 static int ak4104_spi_probe(struct spi_device *spi)
 {
+	struct device_node *np = spi->dev.of_node;
 	struct ak4104_private *ak4104;
 	unsigned int val;
 	int ret;
@@ -225,6 +228,20 @@ static int ak4104_spi_probe(struct spi_device *spi)
 		return ret;
 	}
 
+	if (np) {
+		enum of_gpio_flags flags;
+		int gpio = of_get_named_gpio_flags(np, "reset-gpio", 0, &flags);
+
+		if (gpio_is_valid(gpio)) {
+			ret = devm_gpio_request_one(&spi->dev, gpio,
+				     flags & OF_GPIO_ACTIVE_LOW ?
+					GPIOF_OUT_INIT_LOW : GPIOF_OUT_INIT_HIGH,
+				     "ak4104 reset");
+			if (ret < 0)
+				return ret;
+		}
+	}
+
 	/* read the 'reserved' register - according to the datasheet, it
 	 * should contain 0x5b. Not a good way to verify the presence of
 	 * the device, but there is no hardware ID register. */