iio: Add si7005 relative humidity and temperature sensor driver

sensor provides 12-bit relative humidity and 14-bit temperature
via I2C interface; temperature and linearity compensation is not
implemented (yet)

driver also supports the Si7015, but not the 2nd generation
sensors Si7013/Si7020/Si7021

datasheet is here
http://www.silabs.com/Support%20Documents/TechnicalDocs/Si7005.pdf

v2: (thanks to Lars-Peter Clausen)
* fix coding style
* use devm_iio_device_register()
* change copyright year to 2014
Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/humidity/Kconfig

@@ -12,4 +12,14 @@ config DHT11
 	  Other sensors should work as well as long as they speak the
 	  same protocol.
 
+config SI7005
+	tristate "SI7005 relative humidity and temperature sensor"
+	depends on I2C
+	help
+	  Say yes here to build support for the Silabs Si7005 relative
+	  humidity and temperature sensor.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called si7005.
+
 endmenu

drivers/iio/humidity/Makefile

@@ -3,3 +3,4 @@
 #
 
 obj-$(CONFIG_DHT11) += dht11.o
+obj-$(CONFIG_SI7005) += si7005.o

drivers/iio/humidity/si7005.c

+/*
+ * si7005.c - Support for Silabs Si7005 humidity and temperature sensor
+ *
+ * Copyright (c) 2014 Peter Meerwald <pmeerw@pmeerw.net>
+ *
+ * This file is subject to the terms and conditions of version 2 of
+ * the GNU General Public License.  See the file COPYING in the main
+ * directory of this archive for more details.
+ *
+ * (7-bit I2C slave address 0x40)
+ *
+ * TODO: heater, fast mode, processed mode (temp. / linearity compensation)
+ */
+
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/pm.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+
+#define SI7005_STATUS 0x00
+#define SI7005_DATA 0x01 /* 16-bit, MSB */
+#define SI7005_CONFIG 0x03
+#define SI7005_ID 0x11
+
+#define SI7005_STATUS_NRDY BIT(0)
+#define SI7005_CONFIG_TEMP BIT(4)
+#define SI7005_CONFIG_START BIT(0)
+
+#define SI7005_ID_7005 0x50
+#define SI7005_ID_7015 0xf0
+
+struct si7005_data {
+	struct i2c_client *client;
+	struct mutex lock;
+	u8 config;
+};
+
+static int si7005_read_measurement(struct si7005_data *data, bool temp)
+{
+	int tries = 50;
+	int ret;
+
+	mutex_lock(&data->lock);
+
+	ret = i2c_smbus_write_byte_data(data->client, SI7005_CONFIG,
+		data->config | SI7005_CONFIG_START |
+		(temp ? SI7005_CONFIG_TEMP : 0));
+	if (ret < 0)
+		goto done;
+
+	while (tries-- > 0) {
+		msleep(20);
+		ret = i2c_smbus_read_byte_data(data->client, SI7005_STATUS);
+		if (ret < 0)
+			goto done;
+		if (!(ret & SI7005_STATUS_NRDY))
+			break;
+	}
+	if (tries < 0) {
+		ret = -EIO;
+		goto done;
+	}
+
+	ret = i2c_smbus_read_word_swapped(data->client, SI7005_DATA);
+
+done:
+	mutex_unlock(&data->lock);
+
+	return ret;
+}
+
+static int si7005_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long mask)
+{
+	struct si7005_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = si7005_read_measurement(data, chan->type == IIO_TEMP);
+		if (ret < 0)
+			return ret;
+		*val = ret;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		if (chan->type == IIO_TEMP) {
+			*val = 7;
+			*val2 = 812500;
+		} else {
+			*val = 3;
+			*val2 = 906250;
+		}
+		return IIO_VAL_INT_PLUS_MICRO;
+	case IIO_CHAN_INFO_OFFSET:
+		if (chan->type == IIO_TEMP)
+			*val = -50 * 32 * 4;
+		else
+			*val = -24 * 16 * 16;
+		return IIO_VAL_INT;
+	default:
+		break;
+	}
+
+	return -EINVAL;
+}
+
+static const struct iio_chan_spec si7005_channels[] = {
+	{
+		.type = IIO_HUMIDITYRELATIVE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
+	},
+	{
+		.type = IIO_TEMP,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
+	}
+};
+
+static const struct iio_info si7005_info = {
+	.read_raw = si7005_read_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static int si7005_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct iio_dev *indio_dev;
+	struct si7005_data *data;
+	int ret;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA))
+		return -ENODEV;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	i2c_set_clientdata(client, indio_dev);
+	data->client = client;
+	mutex_init(&data->lock);
+
+	indio_dev->dev.parent = &client->dev;
+	indio_dev->name = dev_name(&client->dev);
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->info = &si7005_info;
+
+	indio_dev->channels = si7005_channels;
+	indio_dev->num_channels = ARRAY_SIZE(si7005_channels);
+
+	ret = i2c_smbus_read_byte_data(client, SI7005_ID);
+	if (ret < 0)
+		return ret;
+	if (ret != SI7005_ID_7005 && ret != SI7005_ID_7015)
+		return -ENODEV;
+
+	ret = i2c_smbus_read_byte_data(client, SI7005_CONFIG);
+	if (ret < 0)
+		return ret;
+	data->config = ret;
+
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct i2c_device_id si7005_id[] = {
+	{ "si7005", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, si7005_id);
+
+static struct i2c_driver si7005_driver = {
+	.driver = {
+		.name	= "si7005",
+		.owner	= THIS_MODULE,
+	},
+	.probe = si7005_probe,
+	.id_table = si7005_id,
+};
+module_i2c_driver(si7005_driver);
+
+MODULE_AUTHOR("Peter Meerwald <pmeerw@pmeerw.net>");
+MODULE_DESCRIPTION("Silabs Si7005 humidity and temperature sensor driver");
+MODULE_LICENSE("GPL");