ASoC: Add reset-gpio DT property to cs4270 driver

In the process of moving over from static board files to the device
tree, reset pins of peripheral reset pins should be handled by their
corresponding drivers.

Add a reset-gpio DT property to the cs4270 driver, and de-assert it
before probing the chip. The logic could be augmented some day to
re-assert it when codec is put to suspend.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

Documentation/devicetree/bindings/sound/cs4270.txt

@@ -8,6 +8,11 @@ Required properties:
 
   - reg : the I2C address of the device for I2C
 
+Optional properties:
+
+  - reset-gpio : a GPIO spec for the reset pin. If specified, it will be
+		 deasserted before communication to the codec starts.
+
 Example:
 
 codec: cs4270@48 {

sound/soc/codecs/cs4270.c

@@ -30,6 +30,7 @@
 #include <linux/delay.h>
 #include <linux/regulator/consumer.h>
 #include <linux/of_device.h>
+#include <linux/of_gpio.h>
 
 /*
  * The codec isn't really big-endian or little-endian, since the I2S
@@ -660,9 +661,25 @@ MODULE_DEVICE_TABLE(of, cs4270_of_match);
 static int cs4270_i2c_probe(struct i2c_client *i2c_client,
 	const struct i2c_device_id *id)
 {
+	struct device_node *np = i2c_client->dev.of_node;
 	struct cs4270_private *cs4270;
 	int ret;
 
+	/* See if we have a way to bring the codec out of reset */
+	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(&i2c_client->dev, gpio,
+				     flags & OF_GPIO_ACTIVE_LOW ?
+					GPIOF_OUT_INIT_LOW : GPIOF_OUT_INIT_HIGH,
+				     "cs4270 reset");
+			if (ret < 0)
+				return ret;
+		}
+	}
+
 	/* Verify that we have a CS4270 */
 
 	ret = i2c_smbus_read_byte_data(i2c_client, CS4270_CHIPID);