iio: bmp280: refactor compensation code

This version of the code avoids extra memory copy operations and is
somewhat smaller in code size.
Signed-off-by: Vlad Dogaru <vlad.dogaru@intel.com>
Acked-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/pressure/bmp280.c

@@ -80,16 +80,12 @@ struct bmp280_data {
 	s32 t_fine;
 };
 
-/* Compensation parameters. */
-struct bmp280_comp_temp {
-	u16 dig_t1;
-	s16 dig_t2, dig_t3;
-};
-
-struct bmp280_comp_press {
-	u16 dig_p1;
-	s16 dig_p2, dig_p3, dig_p4, dig_p5, dig_p6, dig_p7, dig_p8, dig_p9;
-};
+/*
+ * These enums are used for indexing into the array of compensation
+ * parameters.
+ */
+enum { T1, T2, T3 };
+enum { P1, P2, P3, P4, P5, P6, P7, P8, P9 };
 
 static const struct iio_chan_spec bmp280_channels[] = {
 	{
@@ -141,10 +137,18 @@ static const struct regmap_config bmp280_regmap_config = {
 	.volatile_reg = bmp280_is_volatile_reg,
 };
 
-static int bmp280_read_compensation_temp(struct bmp280_data *data,
-					 struct bmp280_comp_temp *comp)
+/*
+ * Returns temperature in DegC, resolution is 0.01 DegC.  Output value of
+ * "5123" equals 51.23 DegC.  t_fine carries fine temperature as global
+ * value.
+ *
+ * Taken from datasheet, Section 3.11.3, "Compensation formula".
+ */
+static s32 bmp280_compensate_temp(struct bmp280_data *data,
+				  s32 adc_temp)
 {
 	int ret;
+	s32 var1, var2, t;
 	__le16 buf[BMP280_COMP_TEMP_REG_COUNT / 2];
 
 	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_TEMP_START,
@@ -155,58 +159,19 @@ static int bmp280_read_compensation_temp(struct bmp280_data *data,
 		return ret;
 	}
 
-	comp->dig_t1 = (u16) le16_to_cpu(buf[0]);
-	comp->dig_t2 = (s16) le16_to_cpu(buf[1]);
-	comp->dig_t3 = (s16) le16_to_cpu(buf[2]);
-
-	return 0;
-}
-
-static int bmp280_read_compensation_press(struct bmp280_data *data,
-					  struct bmp280_comp_press *comp)
-{
-	int ret;
-	__le16 buf[BMP280_COMP_PRESS_REG_COUNT / 2];
-
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_PRESS_START,
-			       buf, BMP280_COMP_PRESS_REG_COUNT);
-	if (ret < 0) {
-		dev_err(&data->client->dev,
-			"failed to read pressure calibration parameters\n");
-		return ret;
-	}
-
-	comp->dig_p1 = (u16) le16_to_cpu(buf[0]);
-	comp->dig_p2 = (s16) le16_to_cpu(buf[1]);
-	comp->dig_p3 = (s16) le16_to_cpu(buf[2]);
-	comp->dig_p4 = (s16) le16_to_cpu(buf[3]);
-	comp->dig_p5 = (s16) le16_to_cpu(buf[4]);
-	comp->dig_p6 = (s16) le16_to_cpu(buf[5]);
-	comp->dig_p7 = (s16) le16_to_cpu(buf[6]);
-	comp->dig_p8 = (s16) le16_to_cpu(buf[7]);
-	comp->dig_p9 = (s16) le16_to_cpu(buf[8]);
-
-	return 0;
-}
-
-/*
- * Returns temperature in DegC, resolution is 0.01 DegC.  Output value of
- * "5123" equals 51.23 DegC.  t_fine carries fine temperature as global
- * value.
+	/*
+	 * The double casts are necessary because le16_to_cpu returns an
+	 * unsigned 16-bit value.  Casting that value directly to a
+	 * signed 32-bit will not do proper sign extension.
 	 *
- * Taken from datasheet, Section 3.11.3, "Compensation formula".
+	 * Conversely, T1 and P1 are unsigned values, so they can be
+	 * cast straight to the larger type.
 	 */
-static s32 bmp280_compensate_temp(struct bmp280_data *data,
-				  struct bmp280_comp_temp *comp,
-				  s32 adc_temp)
-{
-	s32 var1, var2, t;
-
-	var1 = (((adc_temp >> 3) - ((s32) comp->dig_t1 << 1)) *
-		((s32) comp->dig_t2)) >> 11;
-	var2 = (((((adc_temp >> 4) - ((s32) comp->dig_t1)) *
-		  ((adc_temp >> 4) - ((s32) comp->dig_t1))) >> 12) *
-		((s32) comp->dig_t3)) >> 14;
+	var1 = (((adc_temp >> 3) - ((s32)le16_to_cpu(buf[T1]) << 1)) *
+		((s32)(s16)le16_to_cpu(buf[T2]))) >> 11;
+	var2 = (((((adc_temp >> 4) - ((s32)le16_to_cpu(buf[T1]))) *
+		  ((adc_temp >> 4) - ((s32)le16_to_cpu(buf[T1])))) >> 12) *
+		((s32)(s16)le16_to_cpu(buf[T3]))) >> 14;
 
 	data->t_fine = var1 + var2;
 	t = (data->t_fine * 5 + 128) >> 8;
@@ -222,27 +187,36 @@ static s32 bmp280_compensate_temp(struct bmp280_data *data,
  * Taken from datasheet, Section 3.11.3, "Compensation formula".
  */
 static u32 bmp280_compensate_press(struct bmp280_data *data,
-				   struct bmp280_comp_press *comp,
 				   s32 adc_press)
 {
+	int ret;
 	s64 var1, var2, p;
+	__le16 buf[BMP280_COMP_PRESS_REG_COUNT / 2];
 
-	var1 = ((s64) data->t_fine) - 128000;
-	var2 = var1 * var1 * (s64) comp->dig_p6;
-	var2 = var2 + ((var1 * (s64) comp->dig_p5) << 17);
-	var2 = var2 + (((s64) comp->dig_p4) << 35);
-	var1 = ((var1 * var1 * (s64) comp->dig_p3) >> 8) +
-		((var1 * (s64) comp->dig_p2) << 12);
-	var1 = (((((s64) 1) << 47) + var1)) * ((s64) comp->dig_p1) >> 33;
+	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_PRESS_START,
+			       buf, BMP280_COMP_PRESS_REG_COUNT);
+	if (ret < 0) {
+		dev_err(&data->client->dev,
+			"failed to read pressure calibration parameters\n");
+		return ret;
+	}
+
+	var1 = ((s64)data->t_fine) - 128000;
+	var2 = var1 * var1 * (s64)(s16)le16_to_cpu(buf[P6]);
+	var2 = var2 + ((var1 * (s64)(s16)le16_to_cpu(buf[P5])) << 17);
+	var2 = var2 + (((s64)(s16)le16_to_cpu(buf[P4])) << 35);
+	var1 = ((var1 * var1 * (s64)(s16)le16_to_cpu(buf[P3])) >> 8) +
+		((var1 * (s64)(s16)le16_to_cpu(buf[P2])) << 12);
+	var1 = ((((s64)1) << 47) + var1) * ((s64)le16_to_cpu(buf[P1])) >> 33;
 
 	if (var1 == 0)
 		return 0;
 
-	p = ((((s64) 1048576 - adc_press) << 31) - var2) * 3125;
+	p = ((((s64)1048576 - adc_press) << 31) - var2) * 3125;
 	p = div64_s64(p, var1);
-	var1 = (((s64) comp->dig_p9) * (p >> 13) * (p >> 13)) >> 25;
-	var2 = (((s64) comp->dig_p8) * p) >> 19;
-	p = ((p + var1 + var2) >> 8) + (((s64) comp->dig_p7) << 4);
+	var1 = (((s64)(s16)le16_to_cpu(buf[P9])) * (p >> 13) * (p >> 13)) >> 25;
+	var2 = (((s64)(s16)le16_to_cpu(buf[P8])) * p) >> 19;
+	p = ((p + var1 + var2) >> 8) + (((s64)(s16)le16_to_cpu(buf[P7])) << 4);
 
 	return (u32) p;
 }
@@ -253,11 +227,6 @@ static int bmp280_read_temp(struct bmp280_data *data,
 	int ret;
 	__be32 tmp = 0;
 	s32 adc_temp, comp_temp;
-	struct bmp280_comp_temp comp;
-
-	ret = bmp280_read_compensation_temp(data, &comp);
-	if (ret < 0)
-		return ret;
 
 	ret = regmap_bulk_read(data->regmap, BMP280_REG_TEMP_MSB,
 			       (u8 *) &tmp, 3);
@@ -267,7 +236,7 @@ static int bmp280_read_temp(struct bmp280_data *data,
 	}
 
 	adc_temp = be32_to_cpu(tmp) >> 12;
-	comp_temp = bmp280_compensate_temp(data, &comp, adc_temp);
+	comp_temp = bmp280_compensate_temp(data, adc_temp);
 
 	/*
 	 * val might be NULL if we're called by the read_press routine,
@@ -288,11 +257,6 @@ static int bmp280_read_press(struct bmp280_data *data,
 	__be32 tmp = 0;
 	s32 adc_press;
 	u32 comp_press;
-	struct bmp280_comp_press comp;
-
-	ret = bmp280_read_compensation_press(data, &comp);
-	if (ret < 0)
-		return ret;
 
 	/* Read and compensate temperature so we get a reading of t_fine. */
 	ret = bmp280_read_temp(data, NULL);
@@ -307,7 +271,7 @@ static int bmp280_read_press(struct bmp280_data *data,
 	}
 
 	adc_press = be32_to_cpu(tmp) >> 12;
-	comp_press = bmp280_compensate_press(data, &comp, adc_press);
+	comp_press = bmp280_compensate_press(data, adc_press);
 
 	*val = comp_press;
 	*val2 = 256000;