[PATCH v1 13/13] iio: chemical: bme680: Add support for preheat current

[vamoirid <vassilisamir@gmail.com>]

From: Vasileios Amoiridis <vassilisamir@gmail.com>

Add functionality to inject a specified amount of current to the heating
plate before the start of the gas measurement to allow the sensor to reach
faster to the requested temperature.

Signed-off-by: Vasileios Amoiridis <vassilisamir@gmail.com>
---
 drivers/iio/chemical/bme680.h      |  1 +
 drivers/iio/chemical/bme680_core.c | 38 ++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/drivers/iio/chemical/bme680.h b/drivers/iio/chemical/bme680.h
index e7eed2962baa..c658cb631b52 100644
--- a/drivers/iio/chemical/bme680.h
+++ b/drivers/iio/chemical/bme680.h
@@ -42,6 +42,7 @@
 #define   BME680_RHRANGE_MASK			GENMASK(5, 4)
 #define BME680_REG_RES_HEAT_VAL			0x00
 #define   BME680_RSERROR_MASK			GENMASK(7, 4)
+#define BME680_REG_IDAC_HEAT_0			0x50
 #define BME680_REG_RES_HEAT_0			0x5A
 #define BME680_REG_GAS_WAIT_0			0x64
 #define BME680_ADC_GAS_RES			GENMASK(15, 6)
diff --git a/drivers/iio/chemical/bme680_core.c b/drivers/iio/chemical/bme680_core.c
index df6ae4355902..6cdf8b9dbf2b 100644
--- a/drivers/iio/chemical/bme680_core.c
+++ b/drivers/iio/chemical/bme680_core.c
@@ -126,6 +126,7 @@ struct bme680_data {
 	u8 oversampling_temp;
 	u8 oversampling_press;
 	u8 oversampling_humid;
+	u8 preheat_curr;
 	u16 heater_dur;
 	u16 heater_temp;
 
@@ -223,6 +224,12 @@ static const struct iio_chan_spec bme680_channels[] = {
 		},
 	},
 	IIO_CHAN_SOFT_TIMESTAMP(4),
+	{
+		.type = IIO_CURRENT,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.output = 1,
+		.scan_index = 5,
+	},
 };
 
 static int bme680_read_calib(struct bme680_data *data,
@@ -569,6 +576,12 @@ static u8 bme680_calc_heater_dur(u16 dur)
 	return durval;
 }
 
+/* Taken from datasheet, section 5.3.3 */
+static u8 bme680_calc_heater_preheat_current(u8 curr)
+{
+	return 8 * curr - 1;
+}
+
 static int bme680_set_mode(struct bme680_data *data, enum bme680_op_mode mode)
 {
 	struct device *dev = regmap_get_device(data->regmap);
@@ -673,6 +686,19 @@ static int bme680_chip_config(struct bme680_data *data)
 	return 0;
 }
 
+static int bme680_preheat_curr_config(struct bme680_data *data, u8 val)
+{
+	u8 heatr_curr;
+	int ret;
+
+	heatr_curr = bme680_calc_heater_preheat_current(val);
+	ret = regmap_write(data->regmap, BME680_REG_IDAC_HEAT_0, heatr_curr);
+	if (ret < 0)
+		dev_err(data->dev, "failed to write idac_heat_0 register\n");
+
+	return ret;
+}
+
 static int bme680_gas_config(struct bme680_data *data)
 {
 	struct device *dev = regmap_get_device(data->regmap);
@@ -701,6 +727,10 @@ static int bme680_gas_config(struct bme680_data *data)
 		return ret;
 	}
 
+	ret = bme680_preheat_curr_config(data, data->preheat_curr);
+	if (ret)
+		return ret;
+
 	/* Enable the gas sensor and select heater profile set-point 0 */
 	ret = regmap_update_bits(data->regmap, BME680_REG_CTRL_GAS_1,
 				 BME680_RUN_GAS_MASK | BME680_NB_CONV_MASK,
@@ -967,6 +997,13 @@ static int __bme680_write_raw(struct iio_dev *indio_dev,
 
 		return bme680_chip_config(data);
 	}
+	case IIO_CHAN_INFO_RAW:
+	{
+		if (chan->type != IIO_CURRENT)
+			return -EINVAL;
+
+		return bme680_preheat_curr_config(data, (u8)val);
+	}
 	default:
 		return -EINVAL;
 	}
@@ -1199,6 +1236,7 @@ int bme680_core_probe(struct device *dev, struct regmap *regmap,
 	data->oversampling_temp = 8;  /* 8X oversampling rate */
 	data->heater_temp = 320; /* degree Celsius */
 	data->heater_dur = 150;  /* milliseconds */
+	data->preheat_curr = 0; /* milliamps */
 
 	regulator_bulk_set_supply_names(data->supplies, bme680_supply_names,
 					BME680_NUM_SUPPLIES);
-- 
2.43.0