[PATCH v1 17/17] iio: chemical: bme680: Refactorize reading functions

[Vasileios Amoiridis]

The reading of the pressure and humidity value, requires an update
of the t_fine variable which happens by reading the temperature
value.

So the bme680_read_{press/humid}() functions of the above sensors
are internally calling the equivalent bme680_read_temp() function
in order to update the t_fine value. By just looking at the code
this relation is a bit hidden and is not easy to understand why
those channels are not independent.

This commit tries to clear these thing a bit by splitting the
bme680_{read/compensate}_{temp/press/humid}() to the following:

i. bme680_read_{temp/press/humid}_adc(): read the raw value from
the sensor.

ii. bme680_calc_t_fine(): calculate the t_fine variable.

iii. bme680_get_t_fine(): get the t_fine variable.

iv. bme680_compensate_{temp/press/humid}(): compensate the adc
values and return the calculated value.

v. bme680_read_{temp/press/humid}(): combine calls of the
aforementioned functions to return the requested value.

Signed-off-by: Vasileios Amoiridis <vassilisamir@xxxxxxxxx>
---
 drivers/iio/chemical/bme680_core.c | 192 +++++++++++++++++------------
 1 file changed, 116 insertions(+), 76 deletions(-)

diff --git a/drivers/iio/chemical/bme680_core.c b/drivers/iio/chemical/bme680_core.c
index 8f977667249b..cfcb6f791517 100644
--- a/drivers/iio/chemical/bme680_core.c
+++ b/drivers/iio/chemical/bme680_core.c
@@ -104,11 +104,6 @@ struct bme680_data {
 	u8 oversampling_humid;
 	u16 heater_dur;
 	u16 heater_temp;
-	/*
-	 * Carryover value from temperature conversion, used in pressure
-	 * and humidity compensation calculations.
-	 */
-	s32 t_fine;
 
 	/*
 	 * DMA (thus cache coherency maintenance) may require the
@@ -241,6 +236,31 @@ static int bme680_read_calib(struct bme680_data *data,
 	return 0;
 }
 
+static int bme680_read_temp_adc(struct bme680_data *data, u32 *adc_temp)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	u32 value_temp;
+	int ret;
+
+	ret = regmap_bulk_read(data->regmap, BME680_REG_TEMP_MSB,
+			       data->buf, BME680_TEMP_NUM_BYTES);
+	if (ret < 0) {
+		dev_err(dev, "failed to read temperature\n");
+		return ret;
+	}
+
+	value_temp = FIELD_GET(BME680_MEAS_TRIM_MASK,
+			       get_unaligned_be24(data->buf));
+	if (value_temp == BME680_MEAS_SKIPPED) {
+		/* reading was skipped */
+		dev_err(dev, "reading temperature skipped\n");
+		return -EINVAL;
+	}
+	*adc_temp = value_temp;
+
+	return 0;
+}
+
 /*
  * Taken from Bosch BME680 API:
  * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L876
@@ -248,12 +268,10 @@ static int bme680_read_calib(struct bme680_data *data,
  * 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,
-				  u32 adc_temp)
+static s32 bme680_calc_t_fine(struct bme680_data *data, u32 adc_temp)
 {
 	struct bme680_calib *calib = &data->bme680;
 	s64 var1, var2, var3;
-	s16 calc_temp;
 
 	/* If the calibration is invalid, attempt to reload it */
 	if (!calib->par_t2)
@@ -263,10 +281,52 @@ static s16 bme680_compensate_temp(struct bme680_data *data,
 	var2 = (var1 * calib->par_t2) >> 11;
 	var3 = ((var1 >> 1) * (var1 >> 1)) >> 12;
 	var3 = (var3 * ((s32)calib->par_t3 << 4)) >> 14;
-	data->t_fine = var2 + var3;
-	calc_temp = (data->t_fine * 5 + 128) >> 8;
+	return var2 + var3; /* t_fine = var2 + var3 */
+}
 
-	return calc_temp;
+static int bme680_get_t_fine(struct bme680_data *data, s32 *t_fine)
+{
+	u32 adc_temp;
+	int ret;
+
+	ret = bme680_read_temp_adc(data, &adc_temp);
+	if (ret)
+		return ret;
+
+	*t_fine = bme680_calc_t_fine(data, adc_temp);
+
+	return 0;
+}
+
+static s16 bme680_compensate_temp(struct bme680_data *data,
+				  u32 adc_temp)
+{
+	return (bme680_calc_t_fine(data, adc_temp) * 5 + 128) / 256;
+}
+
+static int bme680_read_press_adc(struct bme680_data *data, u32 *adc_press)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	u32 value_press;
+	int ret;
+
+	ret = regmap_bulk_read(data->regmap, BME680_REG_PRESS_MSB,
+			       data->buf, BME680_PRESS_NUM_BYTES);
+	if (ret < 0) {
+		dev_err(dev, "failed to read pressure\n");
+		return ret;
+	}
+
+	value_press = FIELD_GET(BME680_MEAS_TRIM_MASK,
+				get_unaligned_be24(data->buf));
+	if (value_press == BME680_MEAS_SKIPPED) {
+		/* reading was skipped */
+		dev_err(dev, "reading pressure skipped\n");
+		return -EINVAL;
+	}
+	*adc_press = value_press;
+
+	return 0;
 }
 
 /*
@@ -277,12 +337,12 @@ static s16 bme680_compensate_temp(struct bme680_data *data,
  * 97356 Pa = 973.56 hPa.
  */
 static u32 bme680_compensate_press(struct bme680_data *data,
-				   u32 adc_press)
+				   u32 adc_press, s32 t_fine)
 {
 	struct bme680_calib *calib = &data->bme680;
 	s32 var1, var2, var3, press_comp;
 
-	var1 = (data->t_fine >> 1) - 64000;
+	var1 = (t_fine >> 1) - 64000;
 	var2 = ((((var1 >> 2) * (var1 >> 2)) >> 11) * calib->par_p6) >> 2;
 	var2 = var2 + (var1 * calib->par_p5 << 1);
 	var2 = (var2 >> 2) + ((s32)calib->par_p4 << 16);
@@ -310,6 +370,30 @@ static u32 bme680_compensate_press(struct bme680_data *data,
 	return press_comp;
 }
 
+static int bme680_read_humid_adc(struct bme680_data *data, u32 *adc_humidity)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+	u32 value_humidity;
+	int ret;
+
+	ret = regmap_bulk_read(data->regmap, BME680_REG_HUMIDITY_MSB,
+			       &data->be16, BME680_HUMID_NUM_BYTES);
+	if (ret < 0) {
+		dev_err(dev, "failed to read humidity\n");
+		return ret;
+	}
+
+	value_humidity = be16_to_cpu(data->be16);
+	if (value_humidity == BME680_MEAS_SKIPPED) {
+		/* reading was skipped */
+		dev_err(dev, "reading humidity skipped\n");
+		return -EINVAL;
+	}
+	*adc_humidity = value_humidity;
+
+	return 0;
+}
+
 /*
  * Taken from Bosch BME680 API:
  * https://github.com/BoschSensortec/BME680_driver/blob/63bb5336/bme680.c#L937
@@ -318,12 +402,12 @@ static u32 bme680_compensate_press(struct bme680_data *data,
  * value of "43215" represents 43.215 %rH.
  */
 static u32 bme680_compensate_humid(struct bme680_data *data,
-				   u16 adc_humid)
+				   u16 adc_humid, s32 t_fine)
 {
 	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;
+	temp_scaled = (t_fine * 5 + 128) >> 8;
 	var1 = (adc_humid - (((s32)calib->par_h1 * 16))) -
 		(((temp_scaled * calib->par_h3) / 100) >> 1);
 	var2 = (calib->par_h2 *
@@ -555,68 +639,35 @@ static int bme680_gas_config(struct bme680_data *data)
 
 static int bme680_read_temp(struct bme680_data *data, int *val)
 {
-	struct device *dev = regmap_get_device(data->regmap);
 	int ret;
 	u32 adc_temp;
 	s16 comp_temp;
 
-	ret = regmap_bulk_read(data->regmap, BME680_REG_TEMP_MSB,
-			       data->buf, BME680_TEMP_NUM_BYTES);
-	if (ret < 0) {
-		dev_err(dev, "failed to read temperature\n");
+	ret = bme680_read_temp_adc(data, &adc_temp);
+	if (ret)
 		return ret;
-	}
 
-	adc_temp = FIELD_GET(BME680_MEAS_TRIM_MASK,
-			     get_unaligned_be24(data->buf));
-	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 called to get t_fine value used in
-	 * compensate_press/compensate_humid to get compensated
-	 * pressure/humidity readings.
-	 */
-	if (val) {
-		*val = comp_temp * 10; /* Centidegrees to millidegrees */
-		return IIO_VAL_INT;
-	}
-
-	return ret;
+	*val = comp_temp * 10; /* Centidegrees to millidegrees */
+	return IIO_VAL_INT;
 }
 
 static int bme680_read_press(struct bme680_data *data,
 			     int *val, int *val2)
 {
-	struct device *dev = regmap_get_device(data->regmap);
 	int ret;
 	u32 adc_press;
+	s32 t_fine;
 
-	/* Read and compensate temperature to get a reading of t_fine */
-	ret = bme680_read_temp(data, NULL);
-	if (ret < 0)
+	ret = bme680_get_t_fine(data, &t_fine);
+	if (ret)
 		return ret;
 
-	ret = regmap_bulk_read(data->regmap, BME680_REG_PRESS_MSB,
-			       data->buf, BME680_PRESS_NUM_BYTES);
-	if (ret < 0) {
-		dev_err(dev, "failed to read pressure\n");
+	ret = bme680_read_press_adc(data, &adc_press);
+	if (ret)
 		return ret;
-	}
 
-	adc_press = FIELD_GET(BME680_MEAS_TRIM_MASK,
-			      get_unaligned_be24(data->buf));
-	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);
+	*val = bme680_compensate_press(data, adc_press, t_fine);
 	*val2 = 1000;
 	return IIO_VAL_FRACTIONAL;
 }
@@ -624,30 +675,19 @@ static int bme680_read_press(struct bme680_data *data,
 static int bme680_read_humid(struct bme680_data *data,
 			     int *val, int *val2)
 {
-	struct device *dev = regmap_get_device(data->regmap);
 	int ret;
-	u16 adc_humidity;
-	u32 comp_humidity;
+	u32 adc_humidity, comp_humidity;
+	s32 t_fine;
 
-	/* Read and compensate temperature to get a reading of t_fine */
-	ret = bme680_read_temp(data, NULL);
-	if (ret < 0)
+	ret = bme680_get_t_fine(data, &t_fine);
+	if (ret)
 		return ret;
 
-	ret = regmap_bulk_read(data->regmap, BME680_REG_HUMIDITY_MSB,
-			       &data->be16, BME680_HUMID_NUM_BYTES);
-	if (ret < 0) {
-		dev_err(dev, "failed to read humidity\n");
+	ret = bme680_read_humid_adc(data, &adc_humidity);
+	if (ret)
 		return ret;
-	}
 
-	adc_humidity = be16_to_cpu(data->be16);
-	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);
+	comp_humidity = bme680_compensate_humid(data, adc_humidity, t_fine);
 
 	*val = comp_humidity;
 	*val2 = 1000;
-- 
2.25.1