iio: chemical: bme680: Modify startup procedure

Modify the startup procedure to reflect the procedure of the Bosch BME68x
Sensor API. The initial readings and configuration of the sensor need to
happen in the following order:

1) Read calibration data [1,2]
2) Chip general configuration [3]
3) Gas configuration [4]

After the chip configuration it is necessary to ensure that the sensor is
in sleeping mode, in order to apply the gas configuration settings [5].

Also, after the soft reset, it is advised to wait for 5ms [6].

Link: https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/bme68x.c#L162 # [1]
Link: https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/examples/forced_mode/forced_mode.c#L44 # [2]
Link: https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/examples/forced_mode/forced_mode.c#L53 # [3]
Link: https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/examples/forced_mode/forced_mode.c#L60 # [4]
Link: https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/bme68x.c#L640 # [5]
Link: https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/bme68x.c#L294 # [6]
Signed-off-by: Vasileios Amoiridis <vassilisamir@gmail.com>
Link: https://patch.msgid.link/20240609233826.330516-12-vassilisamir@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/chemical/bme680.h

@@ -63,6 +63,8 @@
 
 #define BME680_MEAS_TRIM_MASK			GENMASK(24, 4)
 
+#define BME680_STARTUP_TIME_US			5000
+
 /* Calibration Parameters */
 #define BME680_T2_LSB_REG	0x8A
 #define BME680_H2_MSB_REG	0xE1

drivers/iio/chemical/bme680_core.c

@@ -531,6 +531,11 @@ static int bme680_gas_config(struct bme680_data *data)
 	int ret;
 	u8 heatr_res, heatr_dur;
 
+	/* Go to sleep */
+	ret = bme680_set_mode(data, false);
+	if (ret < 0)
+		return ret;
+
 	heatr_res = bme680_calc_heater_res(data, data->heater_temp);
 
 	/* set target heater temperature */
@@ -866,6 +871,8 @@ int bme680_core_probe(struct device *dev, struct regmap *regmap,
 		return ret;
 	}
 
+	usleep_range(BME680_STARTUP_TIME_US, BME680_STARTUP_TIME_US + 1000);
+
 	ret = regmap_read(regmap, BME680_REG_CHIP_ID, &data->check);
 	if (ret < 0) {
 		dev_err(dev, "Error reading chip ID\n");
@@ -878,22 +885,22 @@ int bme680_core_probe(struct device *dev, struct regmap *regmap,
 		return -ENODEV;
 	}
 
-	ret = bme680_chip_config(data);
+	ret = bme680_read_calib(data, &data->bme680);
 	if (ret < 0) {
-		dev_err(dev, "failed to set chip_config data\n");
+		dev_err(dev,
+			"failed to read calibration coefficients at probe\n");
 		return ret;
 	}
 
-	ret = bme680_gas_config(data);
+	ret = bme680_chip_config(data);
 	if (ret < 0) {
-		dev_err(dev, "failed to set gas config data\n");
+		dev_err(dev, "failed to set chip_config data\n");
 		return ret;
 	}
 
-	ret = bme680_read_calib(data, &data->bme680);
+	ret = bme680_gas_config(data);
 	if (ret < 0) {
-		dev_err(dev,
-			"failed to read calibration coefficients at probe\n");
+		dev_err(dev, "failed to set gas config data\n");
 		return ret;
 	}