iio:dac: Add support for the AD7303

This patch adds support for the AD7303. The AD7303 is a simple 2 channel 8 bit
DAC with an SPI interface.

Signed-off-by: Lars-Peter Clausen <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/dac/ad7303.txt

···
+Analog Devices AD7303 DAC device driver
+
+Required properties:
+	- compatible: Must be "adi,ad7303"
+	- reg: SPI chip select number for the device
+	- spi-max-frequency: Max SPI frequency to use (< 30000000)
+	- Vdd-supply: Phandle to the Vdd power supply
+
+Optional properties:
+	- REF-supply: Phandle to the external reference voltage supply. This should
+	  only be set if there is an external reference voltage connected to the REF
+	  pin. If the property is not set Vdd/2 is used as the reference voltage.
+
+Example:
+
+		ad7303@4 {
+			compatible = "adi,ad7303";
+			reg = <4>;
+			spi-max-frequency = <10000000>;
+			Vdd-supply = <&vdd_supply>;
+			adi,use-external-reference;
+			REF-supply = <&vref_supply>;
+		};

drivers/iio/dac/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad5686.
 
+config AD7303
+	tristate "Analog Devices Analog Devices AD7303 DAC driver"
+	depends on SPI
+	help
+	  Say yes here to build support for Analog Devices AD7303 Digital to Analog
+	  Converters (DAC).
+
+	  To compile this driver as module choose M here: the module will be called
+	  ad7303.
+
 config MAX517
 	tristate "Maxim MAX517/518/519 DAC driver"
 	depends on I2C

drivers/iio/dac/Makefile

···
 obj-$(CONFIG_AD5764) += ad5764.o
 obj-$(CONFIG_AD5791) += ad5791.o
 obj-$(CONFIG_AD5686) += ad5686.o
+obj-$(CONFIG_AD7303) += ad7303.o
 obj-$(CONFIG_MAX517) += max517.o
 obj-$(CONFIG_MCP4725) += mcp4725.o

drivers/iio/dac/ad7303.c

···
+/*
+ * AD7303 Digital to analog converters driver
+ *
+ * Copyright 2013 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2.
+ */
+
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/spi/spi.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+#include <linux/regulator/consumer.h>
+#include <linux/of.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+
+#include <linux/platform_data/ad7303.h>
+
+#define AD7303_CFG_EXTERNAL_VREF BIT(15)
+#define AD7303_CFG_POWER_DOWN(ch) BIT(11 + (ch))
+#define AD7303_CFG_ADDR_OFFSET	10
+
+#define AD7303_CMD_UPDATE_DAC	(0x3 << 8)
+
+/**
+ * struct ad7303_state - driver instance specific data
+ * @spi:		the device for this driver instance
+ * @config:		cached config register value
+ * @dac_cache:		current DAC raw value (chip does not support readback)
+ * @data:		spi transfer buffer
+ */
+
+struct ad7303_state {
+	struct spi_device *spi;
+	uint16_t config;
+	uint8_t dac_cache[2];
+
+	struct regulator *vdd_reg;
+	struct regulator *vref_reg;
+
+	/*
+	 * DMA (thus cache coherency maintenance) requires the
+	 * transfer buffers to live in their own cache lines.
+	 */
+	__be16 data ____cacheline_aligned;
+};
+
+static int ad7303_write(struct ad7303_state *st, unsigned int chan,
+	uint8_t val)
+{
+	st->data = cpu_to_be16(AD7303_CMD_UPDATE_DAC |
+		(chan << AD7303_CFG_ADDR_OFFSET) |
+		st->config | val);
+
+	return spi_write(st->spi, &st->data, sizeof(st->data));
+}
+
+static ssize_t ad7303_read_dac_powerdown(struct iio_dev *indio_dev,
+	uintptr_t private, const struct iio_chan_spec *chan, char *buf)
+{
+	struct ad7303_state *st = iio_priv(indio_dev);
+
+	return sprintf(buf, "%d\n", (bool)(st->config &
+		AD7303_CFG_POWER_DOWN(chan->channel)));
+}
+
+static ssize_t ad7303_write_dac_powerdown(struct iio_dev *indio_dev,
+	 uintptr_t private, const struct iio_chan_spec *chan, const char *buf,
+	 size_t len)
+{
+	struct ad7303_state *st = iio_priv(indio_dev);
+	bool pwr_down;
+	int ret;
+
+	ret = strtobool(buf, &pwr_down);
+	if (ret)
+		return ret;
+
+	mutex_lock(&indio_dev->mlock);
+
+	if (pwr_down)
+		st->config |= AD7303_CFG_POWER_DOWN(chan->channel);
+	else
+		st->config &= ~AD7303_CFG_POWER_DOWN(chan->channel);
+
+	/* There is no noop cmd which allows us to only update the powerdown
+	 * mode, so just write one of the DAC channels again */
+	ad7303_write(st, chan->channel, st->dac_cache[chan->channel]);
+
+	mutex_unlock(&indio_dev->mlock);
+	return ret ? ret : len;
+}
+
+static int ad7303_get_vref(struct ad7303_state *st,
+	struct iio_chan_spec const *chan)
+{
+	int ret;
+
+	if (st->config & AD7303_CFG_EXTERNAL_VREF)
+		return regulator_get_voltage(st->vref_reg);
+
+	ret = regulator_get_voltage(st->vdd_reg);
+	if (ret < 0)
+		return ret;
+	return ret / 2;
+}
+
+static int ad7303_read_raw(struct iio_dev *indio_dev,
+	struct iio_chan_spec const *chan, int *val, int *val2, long info)
+{
+	struct ad7303_state *st = iio_priv(indio_dev);
+	int vref_uv;
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		*val = st->dac_cache[chan->channel];
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		vref_uv = ad7303_get_vref(st, chan);
+		if (vref_uv < 0)
+			return vref_uv;
+
+		*val = 2 * vref_uv / 1000;
+		*val2 = chan->scan_type.realbits;
+
+		return IIO_VAL_FRACTIONAL_LOG2;
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
+static int ad7303_write_raw(struct iio_dev *indio_dev,
+	struct iio_chan_spec const *chan, int val, int val2, long mask)
+{
+	struct ad7303_state *st = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		if (val >= (1 << chan->scan_type.realbits) || val < 0)
+			return -EINVAL;
+
+		mutex_lock(&indio_dev->mlock);
+		ret = ad7303_write(st, chan->address, val);
+		if (ret == 0)
+			st->dac_cache[chan->channel] = val;
+		mutex_unlock(&indio_dev->mlock);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+static const struct iio_info ad7303_info = {
+	.read_raw = ad7303_read_raw,
+	.write_raw = ad7303_write_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static const struct iio_chan_spec_ext_info ad7303_ext_info[] = {
+	{
+		.name = "powerdown",
+		.read = ad7303_read_dac_powerdown,
+		.write = ad7303_write_dac_powerdown,
+	},
+	{ },
+};
+
+#define AD7303_CHANNEL(chan) {					\
+	.type = IIO_VOLTAGE,					\
+	.indexed = 1,						\
+	.output = 1,						\
+	.channel = (chan),					\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
+	.address = (chan),					\
+	.scan_type = {						\
+		.sign = 'u',					\
+		.realbits = '8',				\
+		.storagebits = '8',				\
+		.shift = '0',					\
+	},							\
+	.ext_info = ad7303_ext_info,				\
+}
+
+static const struct iio_chan_spec ad7303_channels[] = {
+	AD7303_CHANNEL(0),
+	AD7303_CHANNEL(1),
+};
+
+static int ad7303_probe(struct spi_device *spi)
+{
+	const struct spi_device_id *id = spi_get_device_id(spi);
+	struct iio_dev *indio_dev;
+	struct ad7303_state *st;
+	bool ext_ref;
+	int ret;
+
+	indio_dev = iio_device_alloc(sizeof(*st));
+	if (indio_dev == NULL)
+		return -ENOMEM;
+
+	st = iio_priv(indio_dev);
+	spi_set_drvdata(spi, indio_dev);
+
+	st->spi = spi;
+
+	st->vdd_reg = regulator_get(&spi->dev, "Vdd");
+	if (IS_ERR(st->vdd_reg)) {
+		ret = PTR_ERR(st->vdd_reg);
+		goto err_free;
+	}
+
+	ret = regulator_enable(st->vdd_reg);
+	if (ret)
+		goto err_put_vdd_reg;
+
+	if (spi->dev.of_node) {
+		ext_ref = of_property_read_bool(spi->dev.of_node,
+				"REF-supply");
+	} else {
+		struct ad7303_platform_data *pdata = spi->dev.platform_data;
+		if (pdata && pdata->use_external_ref)
+			ext_ref = true;
+		else
+		    ext_ref = false;
+	}
+
+	if (ext_ref) {
+		st->vref_reg = regulator_get(&spi->dev, "REF");
+		if (IS_ERR(st->vref_reg))
+			goto err_disable_vdd_reg;
+
+		ret = regulator_enable(st->vref_reg);
+		if (ret)
+			goto err_put_vref_reg;
+
+		st->config |= AD7303_CFG_EXTERNAL_VREF;
+	}
+
+	indio_dev->dev.parent = &spi->dev;
+	indio_dev->name = id->name;
+	indio_dev->info = &ad7303_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = ad7303_channels;
+	indio_dev->num_channels = ARRAY_SIZE(ad7303_channels);
+
+	ret = iio_device_register(indio_dev);
+	if (ret)
+		goto err_disable_vref_reg;
+
+	return 0;
+
+err_disable_vref_reg:
+	if (st->vref_reg)
+		regulator_disable(st->vref_reg);
+err_put_vref_reg:
+	if (st->vref_reg)
+		regulator_put(st->vref_reg);
+err_disable_vdd_reg:
+	regulator_disable(st->vdd_reg);
+err_put_vdd_reg:
+	regulator_put(st->vdd_reg);
+err_free:
+	iio_device_free(indio_dev);
+
+	return ret;
+}
+
+static int ad7303_remove(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev = spi_get_drvdata(spi);
+	struct ad7303_state *st = iio_priv(indio_dev);
+
+	iio_device_unregister(indio_dev);
+
+	if (st->vref_reg) {
+		regulator_disable(st->vref_reg);
+		regulator_put(st->vref_reg);
+	}
+	regulator_disable(st->vdd_reg);
+	regulator_put(st->vdd_reg);
+
+	iio_device_free(indio_dev);
+
+	return 0;
+}
+
+static const struct spi_device_id ad7303_spi_ids[] = {
+	{ "ad7303", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, ad7303_spi_ids);
+
+static struct spi_driver ad7303_driver = {
+	.driver = {
+		.name = "ad7303",
+		.owner = THIS_MODULE,
+	},
+	.probe = ad7303_probe,
+	.remove = ad7303_remove,
+	.id_table = ad7303_spi_ids,
+};
+module_spi_driver(ad7303_driver);
+
+MODULE_AUTHOR("Lars-Peter Clausen <[e-mail]>");
+MODULE_DESCRIPTION("Analog Devices AD7303 DAC driver");
+MODULE_LICENSE("GPL v2");

include/linux/platform_data/ad7303.h

···
+/*
+ * Analog Devices AD7303 DAC driver
+ *
+ * Copyright 2013 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2.
+ */
+
+#ifndef __IIO_ADC_AD7303_H__
+#define __IIO_ADC_AD7303_H__
+
+/**
+ * struct ad7303_platform_data - AD7303 platform data
+ * @use_external_ref: If set to true use an external voltage reference connected
+ * to the REF pin, otherwise use the internal reference derived from Vdd.
+ */
+struct ad7303_platform_data {
+	bool use_external_ref;
+};
+
+#endif