iio: ad9523: support for external signals via gpios

The AD9523 supports external signals for power-down mode, resetting the
device and sync timing.
This change add support for specifying values for these signals via the
gpios and initializing them default values.

For the reset signal, the GPIO is toggled during probing to re-initialize
the device to a known state.
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/frequency/ad9523.c

@@ -12,6 +12,7 @@
 #include <linux/sysfs.h>
 #include <linux/spi/spi.h>
 #include <linux/regulator/consumer.h>
+#include <linux/gpio/consumer.h>
 #include <linux/err.h>
 #include <linux/module.h>
 #include <linux/delay.h>
@@ -268,6 +269,9 @@ struct ad9523_state {
 	struct regulator		*reg;
 	struct ad9523_platform_data	*pdata;
 	struct iio_chan_spec		ad9523_channels[AD9523_NUM_CHAN];
+	struct gpio_desc		*pwrdown_gpio;
+	struct gpio_desc		*reset_gpio;
+	struct gpio_desc		*sync_gpio;
 
 	unsigned long		vcxo_freq;
 	unsigned long		vco_freq;
@@ -988,6 +992,32 @@ static int ad9523_probe(struct spi_device *spi)
 			return ret;
 	}
 
+	st->pwrdown_gpio = devm_gpiod_get_optional(&spi->dev, "powerdown",
+		GPIOD_OUT_HIGH);
+	if (IS_ERR(st->pwrdown_gpio)) {
+		ret = PTR_ERR(st->pwrdown_gpio);
+		goto error_disable_reg;
+	}
+
+	st->reset_gpio = devm_gpiod_get_optional(&spi->dev, "reset",
+		GPIOD_OUT_LOW);
+	if (IS_ERR(st->reset_gpio)) {
+		ret = PTR_ERR(st->reset_gpio);
+		goto error_disable_reg;
+	}
+
+	if (st->reset_gpio) {
+		udelay(1);
+		gpiod_direction_output(st->reset_gpio, 1);
+	}
+
+	st->sync_gpio = devm_gpiod_get_optional(&spi->dev, "sync",
+		GPIOD_OUT_HIGH);
+	if (IS_ERR(st->sync_gpio)) {
+		ret = PTR_ERR(st->sync_gpio);
+		goto error_disable_reg;
+	}
+
 	spi_set_drvdata(spi, indio_dev);
 	st->spi = spi;
 	st->pdata = pdata;