drivers: sensor: bme280: fix "config" register intialization issue

A write to the "ctrl_meas" register can cause the sensor to transition
from sleep to normal mode (which is default Kconfig settings). As per
BME280 datasheet, writes to the "config" register in normal mode may be
ignored. This can lead to use BME280_STANDBY_05MS and BME280_FILTER_OFF
instead of the values set by the application. To fix this, write to the
"config" register before "ctrl_meas" in the sensor init function.

Signed-off-by: Loic Domaigne <tech@domaigne.com>

Author: ljd42

drivers/sensor/bosch/bme280/bme280.c

@@ -348,6 +348,7 @@ static int bme280_chip_init(const struct device *dev)
 		return -ENOTSUP;
 	}
 
+	/* reset the sensor. This will put the sensor is sleep mode */
 	err = bme280_reg_write(dev, BME280_REG_RESET, BME280_CMD_SOFT_RESET);
 	if (err < 0) {
 		LOG_DBG("Soft-reset failed: %d", err);
@@ -373,17 +374,21 @@ static int bme280_chip_init(const struct device *dev)
 		}
 	}
 
-	err = bme280_reg_write(dev, BME280_REG_CTRL_MEAS,
-			       BME280_CTRL_MEAS_VAL);
+	/* Writes to "config" register may be ignored in normal
+	 * mode, but never in sleep mode [datasheet 5.4.6].
+	 *
+	 * So perform "config" write before "ctrl_meas", as "ctrl_meas"
+	 * could cause the sensor to transition from sleep to normal mode.
+	 */
+	err = bme280_reg_write(dev, BME280_REG_CONFIG, BME280_CONFIG_VAL);
 	if (err < 0) {
-		LOG_DBG("CTRL_MEAS write failed: %d", err);
+		LOG_DBG("CONFIG write failed: %d", err);
 		return err;
 	}
 
-	err = bme280_reg_write(dev, BME280_REG_CONFIG,
-			       BME280_CONFIG_VAL);
+	err = bme280_reg_write(dev, BME280_REG_CTRL_MEAS, BME280_CTRL_MEAS_VAL);
 	if (err < 0) {
-		LOG_DBG("CONFIG write failed: %d", err);
+		LOG_DBG("CTRL_MEAS write failed: %d", err);
 		return err;
 	}
 	/* Wait for the sensor to be ready */