diff --git a/Documentation/ABI/testing/sysfs-bus-iio-chemical-sgp40 b/Documentation/ABI/testing/sysfs-bus-iio-chemical-sgp40
new file mode 100644
index 000000000000..469a7c00fad4
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-chemical-sgp40
@@ -0,0 +1,31 @@
+What:		/sys/bus/iio/devices/iio:deviceX/out_temp_raw
+Date:		August 2021
+KernelVersion:	5.15
+Contact:	Andreas Klinger <ak@it-klinger.de>
+Description:
+		Set the temperature. This value is sent to the sensor for
+		temperature compensation.
+		Default value: 25000 (25 °C)
+
+What:		/sys/bus/iio/devices/iio:deviceX/out_humidityrelative_raw
+Date:		August 2021
+KernelVersion:	5.15
+Contact:	Andreas Klinger <ak@it-klinger.de>
+Description:
+		Set the relative humidity. This value is sent to the sensor for
+		humidity compensation.
+		Default value: 50000 (50 % relative humidity)
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_resistance_calibbias
+Date:		August 2021
+KernelVersion:	5.15
+Contact:	Andreas Klinger <ak@it-klinger.de>
+Description:
+		Set the bias value for the resistance which is used for
+		calculation of in_concentration_input as follows:
+
+		x = (in_resistance_raw - in_resistance_calibbias) * 0.65
+
+		in_concentration_input = 500 / (1 + e^x)
+
+		Default value: 30000
diff --git a/MAINTAINERS b/MAINTAINERS
index 19135a9d778e..60f5e57ef385 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16707,6 +16707,12 @@ F:	drivers/iio/chemical/scd30_core.c
 F:	drivers/iio/chemical/scd30_i2c.c
 F:	drivers/iio/chemical/scd30_serial.c
 
+SENSIRION SGP40 GAS SENSOR DRIVER
+M:	Andreas Klinger <ak@it-klinger.de>
+S:	Maintained
+F:	Documentation/ABI/testing/sysfs-bus-iio-chemical-sgp40
+F:	drivers/iio/chemical/sgp40.c
+
 SENSIRION SPS30 AIR POLLUTION SENSOR DRIVER
 M:	Tomasz Duszynski <tduszyns@gmail.com>
 S:	Maintained
diff --git a/drivers/iio/chemical/Kconfig b/drivers/iio/chemical/Kconfig
index a4920646e9be..c03667e62732 100644
--- a/drivers/iio/chemical/Kconfig
+++ b/drivers/iio/chemical/Kconfig
@@ -131,6 +131,17 @@ config SENSIRION_SGP30
 	  To compile this driver as module, choose M here: the
 	  module will be called sgp30.
 
+config SENSIRION_SGP40
+	tristate "Sensirion SGP40 gas sensor"
+	depends on I2C
+	select CRC8
+	help
+	  Say Y here to build I2C interface to support Sensirion SGP40 gas
+	  sensor
+
+	  To compile this driver as module, choose M here: the
+	  module will be called sgp40.
+
 config SPS30
 	tristate
 	select IIO_BUFFER
diff --git a/drivers/iio/chemical/Makefile b/drivers/iio/chemical/Makefile
index 4898690cc155..d07af581f234 100644
--- a/drivers/iio/chemical/Makefile
+++ b/drivers/iio/chemical/Makefile
@@ -16,6 +16,7 @@ obj-$(CONFIG_SCD30_CORE) += scd30_core.o
 obj-$(CONFIG_SCD30_I2C) += scd30_i2c.o
 obj-$(CONFIG_SCD30_SERIAL) += scd30_serial.o
 obj-$(CONFIG_SENSIRION_SGP30)	+= sgp30.o
+obj-$(CONFIG_SENSIRION_SGP40)	+= sgp40.o
 obj-$(CONFIG_SPS30) += sps30.o
 obj-$(CONFIG_SPS30_I2C) += sps30_i2c.o
 obj-$(CONFIG_SPS30_SERIAL) += sps30_serial.o
diff --git a/drivers/iio/chemical/sgp40.c b/drivers/iio/chemical/sgp40.c
new file mode 100644
index 000000000000..fdbe75b56873
--- /dev/null
+++ b/drivers/iio/chemical/sgp40.c
@@ -0,0 +1,372 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * sgp40.c - Support for Sensirion SGP40 Gas Sensor
+ *
+ * Copyright (C) 2021 Andreas Klinger <ak@it-klinger.de>
+ *
+ * I2C slave address: 0x59
+ *
+ * Datasheet can be found here:
+ * https://www.sensirion.com/file/datasheet_sgp40
+ *
+ * There are two functionalities supported:
+ *
+ * 1) read raw logarithmic resistance value from sensor
+ *    --> useful to pass it to the algorithm of the sensor vendor for
+ *    measuring deteriorations and improvements of air quality.
+ *
+ * 2) calculate an estimated absolute voc index (0 - 500 index points) for
+ *    measuring the air quality.
+ *    For this purpose the value of the resistance for which the voc index
+ *    will be 250 can be set up using calibbias.
+ *
+ * Compensation values of relative humidity and temperature can be set up
+ * by writing to the out values of temp and humidityrelative.
+ */
+
+#include <linux/module.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/delay.h>
+#include <linux/mutex.h>
+#include <linux/i2c.h>
+#include <linux/crc8.h>
+
+/*
+ * floating point calculation of voc is done as integer
+ * where numbers are multiplied by 1 << SGP40_CALC_POWER
+ */
+#define SGP40_CALC_POWER	14
+
+#define SGP40_CRC8_POLYNOMIAL	0x31
+#define SGP40_CRC8_INIT		0xff
+
+DECLARE_CRC8_TABLE(sgp40_crc8_table);
+
+struct sgp40_data {
+	struct device		*dev;
+	struct i2c_client	*client;
+	int			rht;
+	int			temp;
+	int			res_calibbias;
+	struct mutex		lock;
+};
+
+struct sgp40_tg_measure {
+	u8	command[2];
+	__be16	rht_ticks;
+	u8	rht_crc;
+	__be16	temp_ticks;
+	u8	temp_crc;
+} __packed;
+
+struct sgp40_tg_result {
+	__be16	res_ticks;
+	u8	res_crc;
+} __packed;
+
+static const struct iio_chan_spec sgp40_channels[] = {
+	{
+		.type = IIO_CONCENTRATION,
+		.channel2 = IIO_MOD_VOC,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
+	},
+	{
+		.type = IIO_RESISTANCE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			BIT(IIO_CHAN_INFO_CALIBBIAS),
+	},
+	{
+		.type = IIO_TEMP,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.output = 1,
+	},
+	{
+		.type = IIO_HUMIDITYRELATIVE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.output = 1,
+	},
+};
+
+/*
+ * taylor approximation of e^x:
+ * y = 1 + x + x^2 / 2 + x^3 / 6 + x^4 / 24 + ... + x^n / n!
+ *
+ * Because we are calculating x real value multiplied by 2^power we get
+ * an additional 2^power^n to divide for every element. For a reasonable
+ * precision this would overflow after a few iterations. Therefore we
+ * divide the x^n part whenever its about to overflow (xmax).
+ */
+
+static u32 sgp40_exp(int exp, u32 power, u32 rounds)
+{
+        u32 x, y, xp;
+        u32 factorial, divider, xmax;
+        int sign = 1;
+	int i; 
+
+        if (exp == 0) 
+                return 1 << power;
+        else if (exp < 0) {
+                sign = -1;
+                exp *= -1;
+        }
+
+        xmax = 0x7FFFFFFF / exp;
+        x = exp;
+        xp = 1; 
+        factorial = 1; 
+        y = 1 << power;
+        divider = 0; 
+
+        for (i = 1; i <= rounds; i++) {
+                xp *= x; 
+                factorial *= i; 
+                y += (xp >> divider) / factorial;
+                divider += power;
+                /* divide when next multiplication would overflow */
+                if (xp >= xmax) {
+                        xp >>= power;
+                        divider -= power;
+                }
+        }
+   
+        if (sign == -1)
+                return (1 << (power * 2)) / y; 
+        else
+                return y; 
+}
+
+static int sgp40_calc_voc(struct sgp40_data *data, u16 resistance_raw, int *voc)
+{
+	int x;
+	u32 exp = 0;
+
+	/* we calculate as a multiple of 16384 (2^14) */
+	mutex_lock(&data->lock);
+	x = ((int)resistance_raw - data->res_calibbias) * 106;
+	mutex_unlock(&data->lock);
+
+	/* voc = 500 / (1 + e^x) */
+	exp = sgp40_exp(x, SGP40_CALC_POWER, 18);
+	*voc = 500 * ((1 << (SGP40_CALC_POWER * 2)) / ((1<<SGP40_CALC_POWER) + exp));
+
+	dev_dbg(data->dev, "raw: %d res_calibbias: %d x: %d exp: %d voc: %d\n",
+				resistance_raw, data->res_calibbias, x, exp, *voc);
+
+	return 0;
+}
+
+static int sgp40_measure_resistance_raw(struct sgp40_data *data, u16 *resistance_raw)
+{
+	int ret;
+	struct i2c_client *client = data->client;
+	u32 ticks;
+	u16 ticks16;
+	u8 crc;
+	struct sgp40_tg_measure tg = {.command = {0x26, 0x0F}};
+	struct sgp40_tg_result tgres;
+
+	mutex_lock(&data->lock);
+	
+	ticks = (data->rht / 10) * 65535 / 10000;
+	ticks16 = (u16)clamp(ticks, 0u, 65535u); /* clamp between 0 .. 100 %rH */
+	tg.rht_ticks = cpu_to_be16(ticks16);
+	tg.rht_crc = crc8(sgp40_crc8_table, (u8 *)&tg.rht_ticks, 2, SGP40_CRC8_INIT);
+
+	ticks = ((data->temp + 45000) / 10 ) * 65535 / 17500;
+	ticks16 = (u16)clamp(ticks, 0u, 65535u); /* clamp between -45 .. +130 °C */
+	tg.temp_ticks = cpu_to_be16(ticks16);
+	tg.temp_crc = crc8(sgp40_crc8_table, (u8 *)&tg.temp_ticks, 2, SGP40_CRC8_INIT);
+
+	mutex_unlock(&data->lock);
+
+	ret = i2c_master_send(client, (const char *)&tg, sizeof(tg));
+	if (ret != sizeof(tg)) {
+		dev_warn(data->dev, "i2c_master_send ret: %d sizeof: %d\n", ret, sizeof(tg));
+		return -EIO;
+	}
+	msleep(30);
+
+	ret = i2c_master_recv(client, (u8 *)&tgres, sizeof(tgres));
+	if (ret < 0)
+		return ret;
+	if (ret != sizeof(tgres)) {
+		dev_warn(data->dev, "i2c_master_recv ret: %d sizeof: %d\n", ret, sizeof(tgres));
+		return -EIO;
+	}
+
+	crc = crc8(sgp40_crc8_table, (u8 *)&tgres.res_ticks, 2, SGP40_CRC8_INIT);
+	if (crc != tgres.res_crc) {
+		dev_err(data->dev, "CRC error while measure-raw\n");
+		return -EIO;
+	}
+
+	*resistance_raw = be16_to_cpu(tgres.res_ticks);
+
+	return 0;
+}
+
+static int sgp40_read_raw(struct iio_dev *indio_dev,
+			struct iio_chan_spec const *chan, int *val,
+			int *val2, long mask)
+{
+	struct sgp40_data *data = iio_priv(indio_dev);
+	int ret, voc;
+	u16 resistance_raw;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		switch (chan->type) {
+		case IIO_RESISTANCE:
+			ret = sgp40_measure_resistance_raw(data, &resistance_raw);
+			if (ret)
+				return ret;
+			*val = resistance_raw;
+			return IIO_VAL_INT;
+		case IIO_TEMP:
+			mutex_lock(&data->lock);
+			*val = data->temp;
+			mutex_unlock(&data->lock);
+			return IIO_VAL_INT;
+		case IIO_HUMIDITYRELATIVE:
+			mutex_lock(&data->lock);
+			*val = data->rht;
+			mutex_unlock(&data->lock);
+			return IIO_VAL_INT;
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_PROCESSED:
+		ret = sgp40_measure_resistance_raw(data, &resistance_raw);
+		if (ret)
+			return ret;
+		ret = sgp40_calc_voc(data, resistance_raw, &voc);
+		if (ret)
+			return ret;
+		*val = voc / (1 << SGP40_CALC_POWER);
+		/*
+		 * calculation should fit into integer, where:
+		 * voc <= (500 * 2^SGP40_CALC_POWER) = 8192000
+		 * (with SGP40_CALC_POWER = 14)
+		 */
+		*val2 = ((voc % (1 << SGP40_CALC_POWER)) * 244) / (1 << (SGP40_CALC_POWER - 12));
+		dev_dbg(data->dev, "voc: %d val: %d.%06d\n", voc, *val, *val2);
+		return IIO_VAL_INT_PLUS_MICRO;
+	case IIO_CHAN_INFO_CALIBBIAS:
+		mutex_lock(&data->lock);
+		*val = data->res_calibbias;
+		mutex_unlock(&data->lock);
+		return IIO_VAL_INT;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int sgp40_write_raw(struct iio_dev *indio_dev,
+			struct iio_chan_spec const *chan, int val,
+			int val2, long mask)
+{
+	struct sgp40_data *data = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		switch (chan->type) {
+		case IIO_TEMP:
+			if ((val < -45000) || (val > 130000))
+				return -EINVAL;
+			mutex_lock(&data->lock);
+			data->temp = val;
+			mutex_unlock(&data->lock);
+			return 0;
+		case IIO_HUMIDITYRELATIVE:
+			if ((val < 0) || (val > 100000))
+				return -EINVAL;
+			mutex_lock(&data->lock);
+			data->rht = val;
+			mutex_unlock(&data->lock);
+			return 0;
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_CALIBBIAS:
+		if ((val < 20000) || (val > 52768))
+			return -EINVAL;
+		mutex_lock(&data->lock);
+		data->res_calibbias = val;
+		mutex_unlock(&data->lock);
+		return 0;
+	}
+	return -EINVAL;
+}
+
+static const struct iio_info sgp40_info = {
+	.read_raw	= sgp40_read_raw,
+	.write_raw	= sgp40_write_raw,
+};
+
+static int sgp40_probe(struct i2c_client *client,
+		     const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct iio_dev *indio_dev;
+	struct sgp40_data *data;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+	data->dev = dev;
+
+	crc8_populate_msb(sgp40_crc8_table, SGP40_CRC8_POLYNOMIAL);
+
+	mutex_init(&data->lock);
+
+	/* set default values */
+	data->rht = 50000;		/* 50 % */
+	data->temp = 25000;		/* 25 °C */
+	data->res_calibbias = 30000;	/* resistance raw value for voc index of 250 */
+
+	indio_dev->info = &sgp40_info;
+	indio_dev->name = id->name;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = sgp40_channels;
+	indio_dev->num_channels = ARRAY_SIZE(sgp40_channels);
+
+	ret = devm_iio_device_register(dev, indio_dev);
+	if (ret)
+		dev_err(dev, "failed to register iio device\n");
+
+	return ret;
+}
+
+static const struct i2c_device_id sgp40_id[] = {
+	{ "sgp40" },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(i2c, sgp40_id);
+
+static const struct of_device_id sgp40_dt_ids[] = {
+	{ .compatible = "sensirion,sgp40" },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(of, sgp40_dt_ids);
+
+static struct i2c_driver sgp40_driver = {
+	.driver = {
+		.name = "sgp40",
+		.of_match_table = sgp40_dt_ids,
+	},
+	.probe = sgp40_probe,
+	.id_table = sgp40_id,
+};
+module_i2c_driver(sgp40_driver);
+
+MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
+MODULE_DESCRIPTION("Sensirion SGP40 gas sensor");
+MODULE_LICENSE("GPL v2");
