iio: chemical: Add support for Bosch BME680 sensor

Bosch BME680 is a 4-in-1 sensor with temperature, pressure, humidity
and gas sensing capability. It supports both I2C and SPI communication
protocol for effective data communication.

The device supports two modes:

1. Sleep mode
2. Forced mode

The measurements only takes place when forced mode is triggered and a
single TPHG cycle is performed by the sensor. The sensor automatically
goes to sleep after afterwards.

The device has various calibration constants/parameters programmed into
devices' non-volatile memory(NVM) during production and can't be altered
by the user. These constants are used in the compensation functions to
get the required compensated readings along with the raw data. The
compensation functions/algorithms are provided by Bosch Sensortec GmbH
via their API[1]. As these don't change during the measurement cycle,
therefore we read and store them at the probe. The default configs
supplied by Bosch are also set at probe.

0-day tested with build success.

GSoC-2018: https://summerofcode.withgoogle.com/projects/#6691473790074880
Mentor: Daniel Baluta
[1] https://github.com/BoschSensortec/BME680_driver
Datasheet:
https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME680-DS001-00.pdf

Note from Jonathan: The compensation functions are 'interesting' and
could do with a tidy up in future.  However, they work so we can leave that
for another day.

Cc: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Himanshu Jha <himanshujha199640@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 959 insertions, 0 deletions

diff --git a/drivers/iio/chemical/bme680_core.c b/drivers/iio/chemical/bme680_core.c
new file mode 100644
index 000000000000..7d9bb62baa3f
--- /dev/null
+++ b/drivers/iio/chemical/bme680_core.c
@@ -0,0 +1,959 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Bosch BME680 - Temperature, Pressure, Humidity & Gas Sensor
+ *
+ * Copyright (C) 2017 - 2018 Bosch Sensortec GmbH
+ * Copyright (C) 2018 Himanshu Jha <himanshujha199640@gmail.com>
+ *
+ * Datasheet:
+ * https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME680-DS001-00.pdf
+ */
+#include <linux/acpi.h>
+#include <linux/bitfield.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/log2.h>
+#include <linux/regmap.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+
+#include "bme680.h"
+
+struct bme680_calib {
+	u16 par_t1;
+	s16 par_t2;
+	s8  par_t3;
+	u16 par_p1;
+	s16 par_p2;
+	s8  par_p3;
+	s16 par_p4;
+	s16 par_p5;
+	s8  par_p6;
+	s8  par_p7;
+	s16 par_p8;
+	s16 par_p9;
+	u8  par_p10;
+	u16 par_h1;
+	u16 par_h2;
+	s8  par_h3;
+	s8  par_h4;
+	s8  par_h5;
+	s8  par_h6;
+	s8  par_h7;
+	s8  par_gh1;
+	s16 par_gh2;
+	s8  par_gh3;
+	u8  res_heat_range;
+	s8  res_heat_val;
+	s8  range_sw_err;
+};
+
+struct bme680_data {
+	struct regmap *regmap;
+	struct bme680_calib bme680;
+	u8 oversampling_temp;
+	u8 oversampling_press;
+	u8 oversampling_humid;
+	u16 heater_dur;
+	u16 heater_temp;
+	/*
+	 * Carryover value from temperature conversion, used in pressure
+	 * and humidity compensation calculations.
+	 */
+	s32 t_fine;
+};
+
+const struct regmap_config bme680_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+EXPORT_SYMBOL(bme680_regmap_config);
+
+static const struct iio_chan_spec bme680_channels[] = {
+	{
+		.type = IIO_TEMP,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
+				      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+	{
+		.type = IIO_PRESSURE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
+				      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+	{
+		.type = IIO_HUMIDITYRELATIVE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
+				      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+	{
+		.type = IIO_RESISTANCE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
+	},
+};
+
+static const int bme680_oversampling_avail[] = { 1, 2, 4, 8, 16 };
+
+static int bme680_read_calib(struct bme680_data *data,
+			     struct bme680_calib *calib)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	unsigned int tmp, tmp_msb, tmp_lsb;
+	int ret;
+	__le16 buf;
+
+	/* Temperature related coefficients */
+	ret = regmap_bulk_read(data->regmap, BME680_T1_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_T1_LSB_REG\n");
+		return ret;
+	}
+	calib->par_t1 = le16_to_cpu(buf);
+
+	ret = regmap_bulk_read(data->regmap, BME680_T2_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_T2_LSB_REG\n");
+		return ret;
+	}
+	calib->par_t2 = le16_to_cpu(buf);
+
+	ret = regmap_read(data->regmap, BME680_T3_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_T3_REG\n");
+		return ret;
+	}
+	calib->par_t3 = tmp;
+
+	/* Pressure related coefficients */
+	ret = regmap_bulk_read(data->regmap, BME680_P1_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P1_LSB_REG\n");
+		return ret;
+	}
+	calib->par_p1 = le16_to_cpu(buf);
+
+	ret = regmap_bulk_read(data->regmap, BME680_P2_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P2_LSB_REG\n");
+		return ret;
+	}
+	calib->par_p2 = le16_to_cpu(buf);
+
+	ret = regmap_read(data->regmap, BME680_P3_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P3_REG\n");
+		return ret;
+	}
+	calib->par_p3 = tmp;
+
+	ret = regmap_bulk_read(data->regmap, BME680_P4_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P4_LSB_REG\n");
+		return ret;
+	}
+	calib->par_p4 = le16_to_cpu(buf);
+
+	ret = regmap_bulk_read(data->regmap, BME680_P5_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P5_LSB_REG\n");
+		return ret;
+	}
+	calib->par_p5 = le16_to_cpu(buf);
+
+	ret = regmap_read(data->regmap, BME680_P6_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P6_REG\n");
+		return ret;
+	}
+	calib->par_p6 = tmp;
+
+	ret = regmap_read(data->regmap, BME680_P7_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P7_REG\n");
+		return ret;
+	}
+	calib->par_p7 = tmp;
+
+	ret = regmap_bulk_read(data->regmap, BME680_P8_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P8_LSB_REG\n");
+		return ret;
+	}
+	calib->par_p8 = le16_to_cpu(buf);
+
+	ret = regmap_bulk_read(data->regmap, BME680_P9_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P9_LSB_REG\n");
+		return ret;
+	}
+	calib->par_p9 = le16_to_cpu(buf);
+
+	ret = regmap_read(data->regmap, BME680_P10_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_P10_REG\n");
+		return ret;
+	}
+	calib->par_p10 = tmp;
+
+	/* Humidity related coefficients */
+	ret = regmap_read(data->regmap, BME680_H1_MSB_REG, &tmp_msb);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H1_MSB_REG\n");
+		return ret;
+	}
+
+	ret = regmap_read(data->regmap, BME680_H1_LSB_REG, &tmp_lsb);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H1_LSB_REG\n");
+		return ret;
+	}
+
+	calib->par_h1 = (tmp_msb << BME680_HUM_REG_SHIFT_VAL) |
+				(tmp_lsb & BME680_BIT_H1_DATA_MSK);
+
+	ret = regmap_read(data->regmap, BME680_H2_MSB_REG, &tmp_msb);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H2_MSB_REG\n");
+		return ret;
+	}
+
+	ret = regmap_read(data->regmap, BME680_H2_LSB_REG, &tmp_lsb);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H2_LSB_REG\n");
+		return ret;
+	}
+
+	calib->par_h2 = (tmp_msb << BME680_HUM_REG_SHIFT_VAL) |
+				(tmp_lsb >> BME680_HUM_REG_SHIFT_VAL);
+
+	ret = regmap_read(data->regmap, BME680_H3_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H3_REG\n");
+		return ret;
+	}
+	calib->par_h3 = tmp;
+
+	ret = regmap_read(data->regmap, BME680_H4_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H4_REG\n");
+		return ret;
+	}
+	calib->par_h4 = tmp;
+
+	ret = regmap_read(data->regmap, BME680_H5_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H5_REG\n");
+		return ret;
+	}
+	calib->par_h5 = tmp;
+
+	ret = regmap_read(data->regmap, BME680_H6_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H6_REG\n");
+		return ret;
+	}
+	calib->par_h6 = tmp;
+
+	ret = regmap_read(data->regmap, BME680_H7_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_H7_REG\n");
+		return ret;
+	}
+	calib->par_h7 = tmp;
+
+	/* Gas heater related coefficients */
+	ret = regmap_read(data->regmap, BME680_GH1_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_GH1_REG\n");
+		return ret;
+	}
+	calib->par_gh1 = tmp;
+
+	ret = regmap_bulk_read(data->regmap, BME680_GH2_LSB_REG,
+			       (u8 *) &buf, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_GH2_LSB_REG\n");
+		return ret;
+	}
+	calib->par_gh2 = le16_to_cpu(buf);
+
+	ret = regmap_read(data->regmap, BME680_GH3_REG, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read BME680_GH3_REG\n");
+		return ret;
+	}
+	calib->par_gh3 = tmp;
+
+	/* Other coefficients */
+	ret = regmap_read(data->regmap, BME680_REG_RES_HEAT_RANGE, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read resistance heat range\n");
+		return ret;
+	}
+	calib->res_heat_range = (tmp & BME680_RHRANGE_MSK) / 16;
+
+	ret = regmap_read(data->regmap, BME680_REG_RES_HEAT_VAL, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read resistance heat value\n");
+		return ret;
+	}
+	calib->res_heat_val = tmp;
+
+	ret = regmap_read(data->regmap, BME680_REG_RANGE_SW_ERR, &tmp);
+	if (ret < 0) {
+		dev_err(dev, "failed to read range software error\n");
+		return ret;
+	}
+	calib->range_sw_err = (tmp & BME680_RSERROR_MSK) / 16;
+
+	return 0;
+}
+
+/*
+ * Taken from Bosch BME680 API:
+ * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L876
+ *
+ * Returns temperature measurement in DegC, resolutions is 0.01 DegC. Therefore,
+ * output value of "3233" represents 32.33 DegC.
+ */
+static s16 bme680_compensate_temp(struct bme680_data *data,
+				  s32 adc_temp)
+{
+	struct bme680_calib *calib = &data->bme680;
+	s64 var1, var2, var3;
+	s16 calc_temp;
+
+	var1 = (adc_temp >> 3) - (calib->par_t1 << 1);
+	var2 = (var1 * calib->par_t2) >> 11;
+	var3 = ((var1 >> 1) * (var1 >> 1)) >> 12;
+	var3 = (var3 * (calib->par_t3 << 4)) >> 14;
+	data->t_fine = var2 + var3;
+	calc_temp = (data->t_fine * 5 + 128) >> 8;
+
+	return calc_temp;
+}
+
+/*
+ * Taken from Bosch BME680 API:
+ * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L896
+ *
+ * Returns pressure measurement in Pa. Output value of "97356" represents
+ * 97356 Pa = 973.56 hPa.
+ */
+static u32 bme680_compensate_press(struct bme680_data *data,
+				   u32 adc_press)
+{
+	struct bme680_calib *calib = &data->bme680;
+	s32 var1, var2, var3, press_comp;
+
+	var1 = (data->t_fine >> 1) - 64000;
+	var2 = ((((var1 >> 2) * (var1 >> 2)) >> 11) * calib->par_p6) >> 2;
+	var2 = var2 + (var1 * calib->par_p5 << 1);
+	var2 = (var2 >> 2) + (calib->par_p4 << 16);
+	var1 = (((((var1 >> 2) * (var1 >> 2)) >> 13) *
+			(calib->par_p3 << 5)) >> 3) +
+			((calib->par_p2 * var1) >> 1);
+	var1 = var1 >> 18;
+	var1 = ((32768 + var1) * calib->par_p1) >> 15;
+	press_comp = 1048576 - adc_press;
+	press_comp = ((press_comp - (var2 >> 12)) * 3125);
+
+	if (press_comp >= BME680_MAX_OVERFLOW_VAL)
+		press_comp = ((press_comp / (u32)var1) << 1);
+	else
+		press_comp = ((press_comp << 1) / (u32)var1);
+
+	var1 = (calib->par_p9 * (((press_comp >> 3) *
+			(press_comp >> 3)) >> 13)) >> 12;
+	var2 = ((press_comp >> 2) * calib->par_p8) >> 13;
+	var3 = ((press_comp >> 8) * (press_comp >> 8) *
+			(press_comp >> 8) * calib->par_p10) >> 17;
+
+	press_comp += (var1 + var2 + var3 + (calib->par_p7 << 7)) >> 4;
+
+	return press_comp;
+}
+
+/*
+ * Taken from Bosch BME680 API:
+ * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L937
+ *
+ * Returns humidity measurement in percent, resolution is 0.001 percent. Output
+ * value of "43215" represents 43.215 %rH.
+ */
+static u32 bme680_compensate_humid(struct bme680_data *data,
+				   u16 adc_humid)
+{
+	struct bme680_calib *calib = &data->bme680;
+	s32 var1, var2, var3, var4, var5, var6, temp_scaled, calc_hum;
+
+	temp_scaled = (data->t_fine * 5 + 128) >> 8;
+	var1 = (adc_humid - ((s32) ((s32) calib->par_h1 * 16))) -
+		(((temp_scaled * (s32) calib->par_h3) / 100) >> 1);
+	var2 = ((s32) calib->par_h2 *
+		(((temp_scaled * calib->par_h4) / 100) +
+		 (((temp_scaled * ((temp_scaled * calib->par_h5) / 100))
+		   >> 6) / 100) + (1 << 14))) >> 10;
+	var3 = var1 * var2;
+	var4 = calib->par_h6 << 7;
+	var4 = (var4 + ((temp_scaled * calib->par_h7) / 100)) >> 4;
+	var5 = ((var3 >> 14) * (var3 >> 14)) >> 10;
+	var6 = (var4 * var5) >> 1;
+	calc_hum = (((var3 + var6) >> 10) * 1000) >> 12;
+
+	if (calc_hum > 100000) /* Cap at 100%rH */
+		calc_hum = 100000;
+	else if (calc_hum < 0)
+		calc_hum = 0;
+
+	return calc_hum;
+}
+
+/*
+ * Taken from Bosch BME680 API:
+ * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L973
+ *
+ * Returns gas measurement in Ohm. Output value of "82986" represent 82986 ohms.
+ */
+static u32 bme680_compensate_gas(struct bme680_data *data, u16 gas_res_adc,
+				 u8 gas_range)
+{
+	struct bme680_calib *calib = &data->bme680;
+	s64 var1;
+	u64 var2;
+	s64 var3;
+	u32 calc_gas_res;
+
+	/* Look up table for the possible gas range values */
+	const u32 lookupTable[16] = {2147483647u, 2147483647u,
+				2147483647u, 2147483647u, 2147483647u,
+				2126008810u, 2147483647u, 2130303777u,
+				2147483647u, 2147483647u, 2143188679u,
+				2136746228u, 2147483647u, 2126008810u,
+				2147483647u, 2147483647u};
+
+	var1 = ((1340 + (5 * (s64) calib->range_sw_err)) *
+			((s64) lookupTable[gas_range])) >> 16;
+	var2 = ((gas_res_adc << 15) - 16777216) + var1;
+	var3 = ((125000 << (15 - gas_range)) * var1) >> 9;
+	var3 += (var2 >> 1);
+	calc_gas_res = div64_s64(var3, (s64) var2);
+
+	return calc_gas_res;
+}
+
+/*
+ * Taken from Bosch BME680 API:
+ * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L1002
+ */
+static u8 bme680_calc_heater_res(struct bme680_data *data, u16 temp)
+{
+	struct bme680_calib *calib = &data->bme680;
+	s32 var1, var2, var3, var4, var5, heatr_res_x100;
+	u8 heatr_res;
+
+	if (temp > 400) /* Cap temperature */
+		temp = 400;
+
+	var1 = (((s32) BME680_AMB_TEMP * calib->par_gh3) / 1000) * 256;
+	var2 = (calib->par_gh1 + 784) * (((((calib->par_gh2 + 154009) *
+						temp * 5) / 100)
+						+ 3276800) / 10);
+	var3 = var1 + (var2 / 2);
+	var4 = (var3 / (calib->res_heat_range + 4));
+	var5 = 131 * calib->res_heat_val + 65536;
+	heatr_res_x100 = ((var4 / var5) - 250) * 34;
+	heatr_res = (heatr_res_x100 + 50) / 100;
+
+	return heatr_res;
+}
+
+/*
+ * Taken from Bosch BME680 API:
+ * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L1188
+ */
+static u8 bme680_calc_heater_dur(u16 dur)
+{
+	u8 durval, factor = 0;
+
+	if (dur >= 0xfc0) {
+		durval = 0xff; /* Max duration */
+	} else {
+		while (dur > 0x3F) {
+			dur = dur / 4;
+			factor += 1;
+		}
+		durval = dur + (factor * 64);
+	}
+
+	return durval;
+}
+
+static int bme680_set_mode(struct bme680_data *data, bool mode)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	int ret;
+
+	if (mode) {
+		ret = regmap_write_bits(data->regmap, BME680_REG_CTRL_MEAS,
+					BME680_MODE_MASK, BME680_MODE_FORCED);
+		if (ret < 0)
+			dev_err(dev, "failed to set forced mode\n");
+
+	} else {
+		ret = regmap_write_bits(data->regmap, BME680_REG_CTRL_MEAS,
+					BME680_MODE_MASK, BME680_MODE_SLEEP);
+		if (ret < 0)
+			dev_err(dev, "failed to set sleep mode\n");
+
+	}
+
+	return ret;
+}
+
+static int bme680_chip_config(struct bme680_data *data)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	int ret;
+	u8 osrs = FIELD_PREP(BME680_OSRS_HUMIDITY_MASK,
+			     data->oversampling_humid + 1);
+	/*
+	 * Highly recommended to set oversampling of humidity before
+	 * temperature/pressure oversampling.
+	 */
+	ret = regmap_update_bits(data->regmap, BME680_REG_CTRL_HUMIDITY,
+				 BME680_OSRS_HUMIDITY_MASK, osrs);
+	if (ret < 0) {
+		dev_err(dev, "failed to write ctrl_hum register\n");
+		return ret;
+	}
+
+	/* IIR filter settings */
+	ret = regmap_update_bits(data->regmap, BME680_REG_CONFIG,
+				 BME680_FILTER_MASK,
+				 BME680_FILTER_COEFF_VAL);
+	if (ret < 0) {
+		dev_err(dev, "failed to write config register\n");
+		return ret;
+	}
+
+	osrs = FIELD_PREP(BME680_OSRS_TEMP_MASK, data->oversampling_temp + 1) |
+	       FIELD_PREP(BME680_OSRS_PRESS_MASK, data->oversampling_press + 1);
+
+	ret = regmap_write_bits(data->regmap, BME680_REG_CTRL_MEAS,
+				BME680_OSRS_TEMP_MASK |
+				BME680_OSRS_PRESS_MASK,
+				osrs);
+	if (ret < 0)
+		dev_err(dev, "failed to write ctrl_meas register\n");
+
+	return ret;
+}
+
+static int bme680_gas_config(struct bme680_data *data)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	int ret;
+	u8 heatr_res, heatr_dur;
+
+	heatr_res = bme680_calc_heater_res(data, data->heater_temp);
+
+	/* set target heater temperature */
+	ret = regmap_write(data->regmap, BME680_REG_RES_HEAT_0, heatr_res);
+	if (ret < 0) {
+		dev_err(dev, "failed to write res_heat_0 register\n");
+		return ret;
+	}
+
+	heatr_dur = bme680_calc_heater_dur(data->heater_dur);
+
+	/* set target heating duration */
+	ret = regmap_write(data->regmap, BME680_REG_GAS_WAIT_0, heatr_dur);
+	if (ret < 0) {
+		dev_err(dev, "failted to write gas_wait_0 register\n");
+		return ret;
+	}
+
+	/* Selecting the runGas and NB conversion settings for the sensor */
+	ret = regmap_update_bits(data->regmap, BME680_REG_CTRL_GAS_1,
+				 BME680_RUN_GAS_MASK | BME680_NB_CONV_MASK,
+				 BME680_RUN_GAS_EN_BIT | BME680_NB_CONV_0_VAL);
+	if (ret < 0)
+		dev_err(dev, "failed to write ctrl_gas_1 register\n");
+
+	return ret;
+}
+
+static int bme680_read_temp(struct bme680_data *data,
+			    int *val, int *val2)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	int ret;
+	__be32 tmp = 0;
+	s32 adc_temp;
+	s16 comp_temp;
+
+	/* set forced mode to trigger measurement */
+	ret = bme680_set_mode(data, true);
+	if (ret < 0)
+		return ret;
+
+	ret = regmap_bulk_read(data->regmap, BME680_REG_TEMP_MSB,
+			       (u8 *) &tmp, 3);
+	if (ret < 0) {
+		dev_err(dev, "failed to read temperature\n");
+		return ret;
+	}
+
+	adc_temp = be32_to_cpu(tmp) >> 12;
+	if (adc_temp == BME680_MEAS_SKIPPED) {
+		/* reading was skipped */
+		dev_err(dev, "reading temperature skipped\n");
+		return -EINVAL;
+	}
+	comp_temp = bme680_compensate_temp(data, adc_temp);
+	/*
+	 * val might be NULL if we're called by the read_press/read_humid
+	 * routine which is callled to get t_fine value used in
+	 * compensate_press/compensate_humid to get compensated
+	 * pressure/humidity readings.
+	 */
+	if (val && val2) {
+		*val = comp_temp;
+		*val2 = 100;
+		return IIO_VAL_FRACTIONAL;
+	}
+
+	return ret;
+}
+
+static int bme680_read_press(struct bme680_data *data,
+			     int *val, int *val2)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	int ret;
+	__be32 tmp = 0;
+	s32 adc_press;
+
+	/* Read and compensate temperature to get a reading of t_fine */
+	ret = bme680_read_temp(data, NULL, NULL);
+	if (ret < 0)
+		return ret;
+
+	ret = regmap_bulk_read(data->regmap, BME680_REG_PRESS_MSB,
+			       (u8 *) &tmp, 3);
+	if (ret < 0) {
+		dev_err(dev, "failed to read pressure\n");
+		return ret;
+	}
+
+	adc_press = be32_to_cpu(tmp) >> 12;
+	if (adc_press == BME680_MEAS_SKIPPED) {
+		/* reading was skipped */
+		dev_err(dev, "reading pressure skipped\n");
+		return -EINVAL;
+	}
+
+	*val = bme680_compensate_press(data, adc_press);
+	*val2 = 100;
+	return IIO_VAL_FRACTIONAL;
+}
+
+static int bme680_read_humid(struct bme680_data *data,
+			     int *val, int *val2)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	int ret;
+	__be16 tmp = 0;
+	s32 adc_humidity;
+	u32 comp_humidity;
+
+	/* Read and compensate temperature to get a reading of t_fine */
+	ret = bme680_read_temp(data, NULL, NULL);
+	if (ret < 0)
+		return ret;
+
+	ret = regmap_bulk_read(data->regmap, BM6880_REG_HUMIDITY_MSB,
+			       (u8 *) &tmp, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read humidity\n");
+		return ret;
+	}
+
+	adc_humidity = be16_to_cpu(tmp);
+	if (adc_humidity == BME680_MEAS_SKIPPED) {
+		/* reading was skipped */
+		dev_err(dev, "reading humidity skipped\n");
+		return -EINVAL;
+	}
+	comp_humidity = bme680_compensate_humid(data, adc_humidity);
+
+	*val = comp_humidity;
+	*val2 = 1000;
+	return IIO_VAL_FRACTIONAL;
+}
+
+static int bme680_read_gas(struct bme680_data *data,
+			   int *val)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	int ret;
+	__be16 tmp = 0;
+	unsigned int check;
+	u16 adc_gas_res;
+	u8 gas_range;
+
+	/* Set heater settings */
+	ret = bme680_gas_config(data);
+	if (ret < 0) {
+		dev_err(dev, "failed to set gas config\n");
+		return ret;
+	}
+
+	/* set forced mode to trigger measurement */
+	ret = bme680_set_mode(data, true);
+	if (ret < 0)
+		return ret;
+
+	ret = regmap_read(data->regmap, BME680_REG_MEAS_STAT_0, &check);
+	if (check & BME680_GAS_MEAS_BIT) {
+		dev_err(dev, "gas measurement incomplete\n");
+		return -EBUSY;
+	}
+
+	ret = regmap_read(data->regmap, BME680_REG_GAS_R_LSB, &check);
+	if (ret < 0) {
+		dev_err(dev, "failed to read gas_r_lsb register\n");
+		return ret;
+	}
+
+	/*
+	 * occurs if either the gas heating duration was insuffient
+	 * to reach the target heater temperature or the target
+	 * heater temperature was too high for the heater sink to
+	 * reach.
+	 */
+	if ((check & BME680_GAS_STAB_BIT) == 0) {
+		dev_err(dev, "heater failed to reach the target temperature\n");
+		return -EINVAL;
+	}
+
+	ret = regmap_bulk_read(data->regmap, BME680_REG_GAS_MSB,
+			       (u8 *) &tmp, 2);
+	if (ret < 0) {
+		dev_err(dev, "failed to read gas resistance\n");
+		return ret;
+	}
+
+	gas_range = check & BME680_GAS_RANGE_MASK;
+	adc_gas_res = be16_to_cpu(tmp) >> BME680_ADC_GAS_RES_SHIFT;
+
+	*val = bme680_compensate_gas(data, adc_gas_res, gas_range);
+	return IIO_VAL_INT;
+}
+
+static int bme680_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan,
+			   int *val, int *val2, long mask)
+{
+	struct bme680_data *data = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_PROCESSED:
+		switch (chan->type) {
+		case IIO_TEMP:
+			return bme680_read_temp(data, val, val2);
+		case IIO_PRESSURE:
+			return bme680_read_press(data, val, val2);
+		case IIO_HUMIDITYRELATIVE:
+			return bme680_read_humid(data, val, val2);
+		case IIO_RESISTANCE:
+			return bme680_read_gas(data, val);
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		switch (chan->type) {
+		case IIO_TEMP:
+			*val = 1 << data->oversampling_temp;
+			return IIO_VAL_INT;
+		case IIO_PRESSURE:
+			*val = 1 << data->oversampling_press;
+			return IIO_VAL_INT;
+		case IIO_HUMIDITYRELATIVE:
+			*val = 1 << data->oversampling_humid;
+			return IIO_VAL_INT;
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int bme680_write_oversampling_ratio_temp(struct bme680_data *data,
+						int val)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(bme680_oversampling_avail); i++) {
+		if (bme680_oversampling_avail[i] == val) {
+			data->oversampling_temp = ilog2(val);
+
+			return bme680_chip_config(data);
+		}
+	}
+
+	return -EINVAL;
+}
+
+static int bme680_write_oversampling_ratio_press(struct bme680_data *data,
+						 int val)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(bme680_oversampling_avail); i++) {
+		if (bme680_oversampling_avail[i] == val) {
+			data->oversampling_press = ilog2(val);
+
+			return bme680_chip_config(data);
+		}
+	}
+
+	return -EINVAL;
+}
+
+static int bme680_write_oversampling_ratio_humid(struct bme680_data *data,
+						 int val)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(bme680_oversampling_avail); i++) {
+		if (bme680_oversampling_avail[i] == val) {
+			data->oversampling_humid = ilog2(val);
+
+			return bme680_chip_config(data);
+		}
+	}
+
+	return -EINVAL;
+}
+
+static int bme680_write_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int val, int val2, long mask)
+{
+	struct bme680_data *data = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		switch (chan->type) {
+		case IIO_TEMP:
+			return bme680_write_oversampling_ratio_temp(data, val);
+		case IIO_PRESSURE:
+			return bme680_write_oversampling_ratio_press(data, val);
+		case IIO_HUMIDITYRELATIVE:
+			return bme680_write_oversampling_ratio_humid(data, val);
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
+
+static const char bme680_oversampling_ratio_show[] = "1 2 4 8 16";
+
+static IIO_CONST_ATTR(oversampling_ratio_available,
+		      bme680_oversampling_ratio_show);
+
+static struct attribute *bme680_attributes[] = {
+	&iio_const_attr_oversampling_ratio_available.dev_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group bme680_attribute_group = {
+	.attrs = bme680_attributes,
+};
+
+static const struct iio_info bme680_info = {
+	.read_raw = &bme680_read_raw,
+	.write_raw = &bme680_write_raw,
+	.attrs = &bme680_attribute_group,
+};
+
+static const char *bme680_match_acpi_device(struct device *dev)
+{
+	const struct acpi_device_id *id;
+
+	id = acpi_match_device(dev->driver->acpi_match_table, dev);
+	if (!id)
+		return NULL;
+
+	return dev_name(dev);
+}
+
+int bme680_core_probe(struct device *dev, struct regmap *regmap,
+		      const char *name)
+{
+	struct iio_dev *indio_dev;
+	struct bme680_data *data;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	if (!name && ACPI_HANDLE(dev))
+		name = bme680_match_acpi_device(dev);
+
+	data = iio_priv(indio_dev);
+	dev_set_drvdata(dev, indio_dev);
+	data->regmap = regmap;
+	indio_dev->dev.parent = dev;
+	indio_dev->name = name;
+	indio_dev->channels = bme680_channels;
+	indio_dev->num_channels = ARRAY_SIZE(bme680_channels);
+	indio_dev->info = &bme680_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+
+	/* default values for the sensor */
+	data->oversampling_humid = ilog2(2); /* 2X oversampling rate */
+	data->oversampling_press = ilog2(4); /* 4X oversampling rate */
+	data->oversampling_temp = ilog2(8);  /* 8X oversampling rate */
+	data->heater_temp = 320; /* degree Celsius */
+	data->heater_dur = 150;  /* milliseconds */
+
+	ret = bme680_chip_config(data);
+	if (ret < 0) {
+		dev_err(dev, "failed to set chip_config data\n");
+		return ret;
+	}
+
+	ret = bme680_gas_config(data);
+	if (ret < 0) {
+		dev_err(dev, "failed to set gas config data\n");
+		return ret;
+	}
+
+	ret = bme680_read_calib(data, &data->bme680);
+	if (ret < 0) {
+		dev_err(dev,
+			"failed to read calibration coefficients at probe\n");
+		return ret;
+	}
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+EXPORT_SYMBOL_GPL(bme680_core_probe);
+
+MODULE_AUTHOR("Himanshu Jha <himanshujha199640@gmail.com>");
+MODULE_DESCRIPTION("Bosch BME680 Driver");
+MODULE_LICENSE("GPL v2");