iio: dac: Add support for external reference voltage through the regulator framework.

Signed-off-by: Silvan Murer <silvan.murer@gmail.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/dac/ltc2632.txt

@@ -12,12 +12,26 @@ Required properties:
 Property rules described in Documentation/devicetree/bindings/spi/spi-bus.txt
 apply. In particular, "reg" and "spi-max-frequency" properties must be given.
 
+Optional properties:
+	- vref-supply: Phandle to the external reference voltage supply. This should
+	  only be set if there is an external reference voltage connected to the VREF
+	  pin. If the property is not set the internal reference is used.
+
 Example:
 
+	vref: regulator-vref {
+		compatible = "regulator-fixed";
+		regulator-name = "vref-ltc2632";
+		regulator-min-microvolt = <1250000>;
+		regulator-max-microvolt = <1250000>;
+		regulator-always-on;
+	};
+
 	spi_master {
 		dac: ltc2632@0 {
 			compatible = "lltc,ltc2632-l12";
 			reg = <0>; /* CS0 */
 			spi-max-frequency = <1000000>;
+			vref-supply = <&vref>; /* optional */
 		};
 	};

drivers/iio/dac/ltc2632.c

@@ -2,6 +2,7 @@
  * LTC2632 Digital to analog convertors spi driver
  *
  * Copyright 2017 Maxime Roussin-Bélanger
+ * expanded by Silvan Murer <silvan.murer@gmail.com>
  *
  * Licensed under the GPL-2.
  */
@@ -10,6 +11,7 @@
 #include <linux/spi/spi.h>
 #include <linux/module.h>
 #include <linux/iio/iio.h>
+#include <linux/regulator/consumer.h>
 
 #define LTC2632_DAC_CHANNELS                    2
 
@@ -28,7 +30,7 @@
 /**
  * struct ltc2632_chip_info - chip specific information
  * @channels:		channel spec for the DAC
- * @vref_mv:		reference voltage
+ * @vref_mv:		internal reference voltage
  */
 struct ltc2632_chip_info {
 	const struct iio_chan_spec *channels;
@@ -39,10 +41,14 @@ struct ltc2632_chip_info {
  * struct ltc2632_state - driver instance specific data
  * @spi_dev:			pointer to the spi_device struct
  * @powerdown_cache_mask	used to show current channel powerdown state
+ * @vref_mv			used reference voltage (internal or external)
+ * @vref_reg		regulator for the reference voltage
  */
 struct ltc2632_state {
 	struct spi_device *spi_dev;
 	unsigned int powerdown_cache_mask;
+	int vref_mv;
+	struct regulator *vref_reg;
 };
 
 enum ltc2632_supported_device_ids {
@@ -90,7 +96,7 @@ static int ltc2632_read_raw(struct iio_dev *indio_dev,
 
 	switch (m) {
 	case IIO_CHAN_INFO_SCALE:
-		*val = chip_info->vref_mv;
+		*val = st->vref_mv;
 		*val2 = chan->scan_type.realbits;
 		return IIO_VAL_FRACTIONAL_LOG2;
 	}
@@ -246,6 +252,45 @@ static int ltc2632_probe(struct spi_device *spi)
 	chip_info = (struct ltc2632_chip_info *)
 			spi_get_device_id(spi)->driver_data;
 
+	st->vref_reg = devm_regulator_get_optional(&spi->dev, "vref");
+	if (PTR_ERR(st->vref_reg) == -ENODEV) {
+		/* use internal reference voltage */
+		st->vref_reg = NULL;
+		st->vref_mv = chip_info->vref_mv;
+
+		ret = ltc2632_spi_write(spi, LTC2632_CMD_INTERNAL_REFER,
+				0, 0, 0);
+		if (ret) {
+			dev_err(&spi->dev,
+				"Set internal reference command failed, %d\n",
+				ret);
+			return ret;
+		}
+	} else if (IS_ERR(st->vref_reg)) {
+		dev_err(&spi->dev,
+				"Error getting voltage reference regulator\n");
+		return PTR_ERR(st->vref_reg);
+	} else {
+		/* use external reference voltage */
+		ret = regulator_enable(st->vref_reg);
+		if (ret) {
+			dev_err(&spi->dev,
+				"enable reference regulator failed, %d\n",
+				ret);
+			return ret;
+		}
+		st->vref_mv = regulator_get_voltage(st->vref_reg) / 1000;
+
+		ret = ltc2632_spi_write(spi, LTC2632_CMD_EXTERNAL_REFER,
+				0, 0, 0);
+		if (ret) {
+			dev_err(&spi->dev,
+				"Set external reference command failed, %d\n",
+				ret);
+			return ret;
+		}
+	}
+
 	indio_dev->dev.parent = &spi->dev;
 	indio_dev->name = dev_of_node(&spi->dev) ? dev_of_node(&spi->dev)->name
 						 : spi_get_device_id(spi)->name;
@@ -254,14 +299,20 @@ static int ltc2632_probe(struct spi_device *spi)
 	indio_dev->channels = chip_info->channels;
 	indio_dev->num_channels = LTC2632_DAC_CHANNELS;
 
-	ret = ltc2632_spi_write(spi, LTC2632_CMD_INTERNAL_REFER, 0, 0, 0);
-	if (ret) {
-		dev_err(&spi->dev,
-			"Set internal reference command failed, %d\n", ret);
-		return ret;
-	}
+	return iio_device_register(indio_dev);
+}
+
+static int ltc2632_remove(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev = spi_get_drvdata(spi);
+	struct ltc2632_state *st = iio_priv(indio_dev);
+
+	iio_device_unregister(indio_dev);
+
+	if (st->vref_reg)
+		regulator_disable(st->vref_reg);
 
-	return devm_iio_device_register(&spi->dev, indio_dev);
+	return 0;
 }
 
 static const struct spi_device_id ltc2632_id[] = {
@@ -305,6 +356,7 @@ static struct spi_driver ltc2632_driver = {
 		.of_match_table = of_match_ptr(ltc2632_of_match),
 	},
 	.probe		= ltc2632_probe,
+	.remove		= ltc2632_remove,
 	.id_table	= ltc2632_id,
 };
 module_spi_driver(ltc2632_driver);