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>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/iio/chemical/Kconfig b/drivers/iio/chemical/Kconfig
index cea7f9857a1f..4d799b5cceac 100644
--- a/drivers/iio/chemical/Kconfig
+++ b/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