iio: Add LTC2471/LTC2473 driver

The LTC2741 and LTC2473 are single voltage ADC chips. The LTC2473
is similar to the LTC2471 but outputs a signed differential value.

Datasheet:
  http://cds.linear.com/docs/en/datasheet/24713fb.pdf

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/Kconfig

@@ -362,6 +362,16 @@ config LPC32XX_ADC
 	  activate only one via device tree selection.  Provides direct access
 	  via sysfs.
 
+config LTC2471
+	tristate "Linear Technology LTC2471 and LTC2473 ADC driver"
+	depends on I2C
+	help
+	  Say yes here to build support for Linear Technology LTC2471 and
+	  LTC2473 16-bit I2C ADC.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called ltc2471.
+
 config LTC2485
 	tristate "Linear Technology LTC2485 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -34,6 +34,7 @@ obj-$(CONFIG_INA2XX_ADC) += ina2xx-adc.o
 obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
 obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
 obj-$(CONFIG_LPC32XX_ADC) += lpc32xx_adc.o
+obj-$(CONFIG_LTC2471) += ltc2471.o
 obj-$(CONFIG_LTC2485) += ltc2485.o
 obj-$(CONFIG_LTC2497) += ltc2497.o
 obj-$(CONFIG_MAX1027) += max1027.o

drivers/iio/adc/ltc2471.c

@@ -0,0 +1,160 @@
+/*
+ * Driver for Linear Technology LTC2471 and LTC2473 voltage monitors
+ * The LTC2473 is identical to the 2471, but reports a differential signal.
+ *
+ * Copyright (C) 2017 Topic Embedded Products
+ * Author: Mike Looijmans <mike.looijmans@topic.nl>
+ *
+ * License: GPLv2
+ */
+
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+
+enum ltc2471_chips {
+	ltc2471,
+	ltc2473,
+};
+
+struct ltc2471_data {
+	struct i2c_client *client;
+};
+
+/* Reference voltage is 1.25V */
+#define LTC2471_VREF 1250
+
+/* Read two bytes from the I2C bus to obtain the ADC result */
+static int ltc2471_get_value(struct i2c_client *client)
+{
+	int ret;
+	__be16 buf;
+
+	ret = i2c_master_recv(client, (char *)&buf, sizeof(buf));
+	if (ret < 0)
+		return ret;
+	if (ret != sizeof(buf))
+		return -EIO;
+
+	/* MSB first */
+	return be16_to_cpu(buf);
+}
+
+static int ltc2471_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2, long info)
+{
+	struct ltc2471_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		ret = ltc2471_get_value(data->client);
+		if (ret < 0)
+			return ret;
+		*val = ret;
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		if (chan->differential)
+			/* Output ranges from -VREF to +VREF */
+			*val = 2 * LTC2471_VREF;
+		else
+			/* Output ranges from 0 to VREF */
+			*val = LTC2471_VREF;
+		*val2 = 16;	/* 16 data bits */
+		return IIO_VAL_FRACTIONAL_LOG2;
+
+	case IIO_CHAN_INFO_OFFSET:
+		/* Only differential chip has this property */
+		*val = -LTC2471_VREF;
+		return IIO_VAL_INT;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_chan_spec ltc2471_channel[] = {
+	{
+		.type = IIO_VOLTAGE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+	},
+};
+
+static const struct iio_chan_spec ltc2473_channel[] = {
+	{
+		.type = IIO_VOLTAGE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |
+					    BIT(IIO_CHAN_INFO_OFFSET),
+		.differential = 1,
+	},
+};
+
+static const struct iio_info ltc2471_info = {
+	.read_raw = ltc2471_read_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static int ltc2471_i2c_probe(struct i2c_client *client,
+			     const struct i2c_device_id *id)
+{
+	struct iio_dev *indio_dev;
+	struct ltc2471_data *data;
+	int ret;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -EOPNOTSUPP;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+
+	indio_dev->dev.parent = &client->dev;
+	indio_dev->name = id->name;
+	indio_dev->info = &ltc2471_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	if (id->driver_data == ltc2473)
+		indio_dev->channels = ltc2473_channel;
+	else
+		indio_dev->channels = ltc2471_channel;
+	indio_dev->num_channels = 1;
+
+	/* Trigger once to start conversion and check if chip is there */
+	ret = ltc2471_get_value(client);
+	if (ret < 0) {
+		dev_err(&client->dev, "Cannot read from device.\n");
+		return ret;
+	}
+
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct i2c_device_id ltc2471_i2c_id[] = {
+	{ "ltc2471", ltc2471 },
+	{ "ltc2473", ltc2473 },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, ltc2471_i2c_id);
+
+static struct i2c_driver ltc2471_i2c_driver = {
+	.driver = {
+		.name = "ltc2471",
+	},
+	.probe    = ltc2471_i2c_probe,
+	.id_table = ltc2471_i2c_id,
+};
+
+module_i2c_driver(ltc2471_i2c_driver);
+
+MODULE_DESCRIPTION("LTC2471/LTC2473 ADC driver");
+MODULE_AUTHOR("Topic Embedded Products");
+MODULE_LICENSE("GPL v2");