iio: chemical: ccs811: Add support for AMS CCS811 VOC sensor

Add support for CCS811 VOC sensor. This patch adds support
for reading current and voltage across the sensor and TVOC
and equivalent CO2 values.

Scale and offset values have been computed according to datasheet:
    - For current: raw value is in microamps
        => 0.001 scale to convert to milliamps
    - For voltage: 1.65V = 1023, therefore 1650mV = 1023
        => 1650.0/1023 = 1.612903 scale to convert to millivolts
    - For eCO2: raw value range is from 400ppm to 8192ppm.
        => (val - 400) * (100 - 0) / (8192 - 400) + 0 =
           (val - 400) * 0.01283367 => offset: -400, scale = 0.012834
           to get a percentage value
    -For TVOC: raw value range is from 0ppb to 1187ppb.
        => (val - 0) * 100 / (1187 - 0) + 0 = val * 0.0842459 =>
            scale = 0.084246 for getting a percentage value

Cc: Daniel Baluta <daniel.baluta@gmail.com>
Cc: Alison Schofield <amsfield22@gmail.com>
Signed-off-by: Narcisa Ana Maria Vasile <narcisaanamaria12@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/chemical/Kconfig

@@ -21,6 +21,13 @@ config ATLAS_PH_SENSOR
 	 To compile this driver as module, choose M here: the
 	 module will be called atlas-ph-sensor.
 
+config CCS811
+	tristate "AMS CCS811 VOC sensor"
+	depends on I2C
+	help
+	  Say Y here to build I2C interface support for the AMS
+	  CCS811 VOC (Volatile Organic Compounds) sensor
+
 config IAQCORE
 	tristate "AMS iAQ-Core VOC sensors"
 	depends on I2C

drivers/iio/chemical/Makefile

@@ -4,5 +4,6 @@
 
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_ATLAS_PH_SENSOR)	+= atlas-ph-sensor.o
+obj-$(CONFIG_CCS811)		+= ccs811.o
 obj-$(CONFIG_IAQCORE)		+= ams-iaq-core.o
 obj-$(CONFIG_VZ89X)		+= vz89x.o

drivers/iio/chemical/ccs811.c

+/*
+ * ccs811.c - Support for AMS CCS811 VOC Sensor
+ *
+ * Copyright (C) 2017 Narcisa Vasile <narcisaanamaria12@gmail.com>
+ *
+ * Datasheet: ams.com/content/download/951091/2269479/CCS811_DS000459_3-00.pdf
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * IIO driver for AMS CCS811 (I2C address 0x5A/0x5B set by ADDR Low/High)
+ *
+ * TODO:
+ * 1. Make the drive mode selectable form userspace
+ * 2. Add support for interrupts
+ * 3. Adjust time to wait for data to be ready based on selected operation mode
+ * 4. Read error register and put the information in logs
+ */
+
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/iio/iio.h>
+#include <linux/module.h>
+
+#define CCS811_STATUS		0x00
+#define CCS811_MEAS_MODE	0x01
+#define CCS811_ALG_RESULT_DATA	0x02
+#define CCS811_RAW_DATA		0x03
+#define CCS811_HW_ID		0x20
+#define CCS881_HW_ID_VALUE	0x81
+#define CCS811_HW_VERSION	0x21
+#define CCS811_HW_VERSION_VALUE	0x10
+#define CCS811_HW_VERSION_MASK	0xF0
+#define CCS811_ERR		0xE0
+/* Used to transition from boot to application mode */
+#define CCS811_APP_START	0xF4
+
+/* Status register flags */
+#define CCS811_STATUS_ERROR		BIT(0)
+#define CCS811_STATUS_DATA_READY	BIT(3)
+#define CCS811_STATUS_APP_VALID_MASK	BIT(4)
+#define CCS811_STATUS_APP_VALID_LOADED	BIT(4)
+/*
+ * Value of FW_MODE bit of STATUS register describes the sensor's state:
+ * 0: Firmware is in boot mode, this allows new firmware to be loaded
+ * 1: Firmware is in application mode. CCS811 is ready to take ADC measurements
+ */
+#define CCS811_STATUS_FW_MODE_MASK	BIT(7)
+#define CCS811_STATUS_FW_MODE_APPLICATION	BIT(7)
+
+/* Measurement modes */
+#define CCS811_MODE_IDLE	0x00
+#define CCS811_MODE_IAQ_1SEC	0x10
+#define CCS811_MODE_IAQ_10SEC	0x20
+#define CCS811_MODE_IAQ_60SEC	0x30
+#define CCS811_MODE_RAW_DATA	0x40
+
+#define CCS811_VOLTAGE_MASK	0x3FF
+
+struct ccs811_reading {
+	__be16 co2;
+	__be16 voc;
+	u8 status;
+	u8 error;
+	__be16 resistance;
+} __attribute__((__packed__));
+
+struct ccs811_data {
+	struct i2c_client *client;
+	struct mutex lock; /* Protect readings */
+	struct ccs811_reading buffer;
+};
+
+static const struct iio_chan_spec ccs811_channels[] = {
+	{
+		.type = IIO_CURRENT,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE)
+	}, {
+		.type = IIO_VOLTAGE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE)
+	}, {
+		.type = IIO_CONCENTRATION,
+		.channel2 = IIO_MOD_CO2,
+		.modified = 1,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_OFFSET) |
+				      BIT(IIO_CHAN_INFO_SCALE)
+	}, {
+		.type = IIO_CONCENTRATION,
+		.channel2 = IIO_MOD_VOC,
+		.modified = 1,
+		.info_mask_separate =  BIT(IIO_CHAN_INFO_RAW) |
+				       BIT(IIO_CHAN_INFO_SCALE)
+	},
+};
+
+/*
+ * The CCS811 powers-up in boot mode. A setup write to CCS811_APP_START will
+ * transition the sensor to application mode.
+ */
+static int ccs811_start_sensor_application(struct i2c_client *client)
+{
+	int ret;
+
+	ret = i2c_smbus_read_byte_data(client, CCS811_STATUS);
+	if (ret < 0)
+		return ret;
+
+	if ((ret & CCS811_STATUS_APP_VALID_MASK) !=
+	    CCS811_STATUS_APP_VALID_LOADED)
+		return -EIO;
+
+	ret = i2c_smbus_write_byte(client, CCS811_APP_START);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_read_byte_data(client, CCS811_STATUS);
+	if (ret < 0)
+		return ret;
+
+	if ((ret & CCS811_STATUS_FW_MODE_MASK) !=
+	    CCS811_STATUS_FW_MODE_APPLICATION) {
+		dev_err(&client->dev, "Application failed to start. Sensor is still in boot mode.\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int ccs811_setup(struct i2c_client *client)
+{
+	int ret;
+
+	ret = ccs811_start_sensor_application(client);
+	if (ret < 0)
+		return ret;
+
+	return i2c_smbus_write_byte_data(client, CCS811_MEAS_MODE,
+					 CCS811_MODE_IAQ_1SEC);
+}
+
+static int ccs811_get_measurement(struct ccs811_data *data)
+{
+	int ret, tries = 11;
+
+	/* Maximum waiting time: 1s, as measurements are made every second */
+	while (tries-- > 0) {
+		ret = i2c_smbus_read_byte_data(data->client, CCS811_STATUS);
+		if (ret < 0)
+			return ret;
+
+		if ((ret & CCS811_STATUS_DATA_READY) || tries == 0)
+			break;
+		msleep(100);
+	}
+	if (!(ret & CCS811_STATUS_DATA_READY))
+		return -EIO;
+
+	return i2c_smbus_read_i2c_block_data(data->client,
+					    CCS811_ALG_RESULT_DATA, 8,
+					    (char *)&data->buffer);
+}
+
+static int ccs811_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan,
+			   int *val, int *val2, long mask)
+{
+	struct ccs811_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		mutex_lock(&data->lock);
+		ret = ccs811_get_measurement(data);
+		if (ret < 0) {
+			mutex_unlock(&data->lock);
+			return ret;
+		}
+
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			*val = be16_to_cpu(data->buffer.resistance) &
+					   CCS811_VOLTAGE_MASK;
+			ret = IIO_VAL_INT;
+			break;
+		case IIO_CURRENT:
+			*val = be16_to_cpu(data->buffer.resistance) >> 10;
+			ret = IIO_VAL_INT;
+			break;
+		case IIO_CONCENTRATION:
+			switch (chan->channel2) {
+			case IIO_MOD_CO2:
+				*val = be16_to_cpu(data->buffer.co2);
+				ret =  IIO_VAL_INT;
+				break;
+			case IIO_MOD_VOC:
+				*val = be16_to_cpu(data->buffer.voc);
+				ret = IIO_VAL_INT;
+				break;
+			default:
+				ret = -EINVAL;
+			}
+			break;
+		default:
+			ret = -EINVAL;
+		}
+		mutex_unlock(&data->lock);
+
+		return ret;
+
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			*val = 1;
+			*val2 = 612903;
+			return IIO_VAL_INT_PLUS_MICRO;
+		case IIO_CURRENT:
+			*val = 0;
+			*val2 = 1000;
+			return IIO_VAL_INT_PLUS_MICRO;
+		case IIO_CONCENTRATION:
+			switch (chan->channel2) {
+			case IIO_MOD_CO2:
+				*val = 0;
+				*val2 = 12834;
+				return IIO_VAL_INT_PLUS_MICRO;
+			case IIO_MOD_VOC:
+				*val = 0;
+				*val2 = 84246;
+				return IIO_VAL_INT_PLUS_MICRO;
+			default:
+				return -EINVAL;
+			}
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_OFFSET:
+		if (!(chan->type == IIO_CONCENTRATION &&
+		      chan->channel2 == IIO_MOD_CO2))
+			return -EINVAL;
+		*val = -400;
+		return IIO_VAL_INT;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ccs811_info = {
+	.read_raw = ccs811_read_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static int ccs811_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	struct iio_dev *indio_dev;
+	struct ccs811_data *data;
+	int ret;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WRITE_BYTE
+				     | I2C_FUNC_SMBUS_BYTE_DATA
+				     | I2C_FUNC_SMBUS_READ_I2C_BLOCK))
+		return -EOPNOTSUPP;
+
+	/* Check hardware id (should be 0x81 for this family of devices) */
+	ret = i2c_smbus_read_byte_data(client, CCS811_HW_ID);
+	if (ret < 0)
+		return ret;
+
+	if (ret != CCS881_HW_ID_VALUE) {
+		dev_err(&client->dev, "hardware id doesn't match CCS81x\n");
+		return -ENODEV;
+	}
+
+	ret = i2c_smbus_read_byte_data(client, CCS811_HW_VERSION);
+	if (ret < 0)
+		return ret;
+
+	if ((ret & CCS811_HW_VERSION_MASK) != CCS811_HW_VERSION_VALUE) {
+		dev_err(&client->dev, "no CCS811 sensor\n");
+		return -ENODEV;
+	}
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	ret = ccs811_setup(client);
+	if (ret < 0)
+		return ret;
+
+	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 = id->name;
+	indio_dev->info = &ccs811_info;
+
+	indio_dev->channels = ccs811_channels;
+	indio_dev->num_channels = ARRAY_SIZE(ccs811_channels);
+
+	return iio_device_register(indio_dev);
+}
+
+static int ccs811_remove(struct i2c_client *client)
+{
+	struct iio_dev *indio_dev = i2c_get_clientdata(client);
+
+	iio_device_unregister(indio_dev);
+
+	return i2c_smbus_write_byte_data(client, CCS811_MEAS_MODE,
+					 CCS811_MODE_IDLE);
+}
+
+static const struct i2c_device_id ccs811_id[] = {
+	{"ccs811", 0},
+	{	}
+};
+MODULE_DEVICE_TABLE(i2c, ccs811_id);
+
+static struct i2c_driver ccs811_driver = {
+	.driver = {
+		.name = "ccs811",
+	},
+	.probe = ccs811_probe,
+	.remove = ccs811_remove,
+	.id_table = ccs811_id,
+};
+module_i2c_driver(ccs811_driver);
+
+MODULE_AUTHOR("Narcisa Vasile <narcisaanamaria12@gmail.com>");
+MODULE_DESCRIPTION("CCS811 volatile organic compounds sensor");
+MODULE_LICENSE("GPL v2");