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>

1 files changed, 52 insertions, 88 deletions

diff --git a/drivers/iio/pressure/bmp280.c b/drivers/iio/pressure/bmp280.c
index 75038dacfff1..47dfd347f66f 100644
--- a/drivers/iio/pressure/bmp280.c
+++ b/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[] = {
         {
@@ -141,54 +137,6 @@ 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)
-{
-        int ret;
-        __le16 buf[BMP280_COMP_TEMP_REG_COUNT / 2];
-
-        ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_TEMP_START,
-                               buf, BMP280_COMP_TEMP_REG_COUNT);
-        if (ret < 0) {
-                dev_err(&data->client->dev,
-                        "failed to read temperature calibration parameters\n");
-                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
@@ -197,16 +145,33 @@ static int bmp280_read_compensation_press(struct bmp280_data *data,
  * Taken from datasheet, Section 3.11.3, "Compensation formula".
  */
 static s32 bmp280_compensate_temp(struct bmp280_data *data,
-                                  struct bmp280_comp_temp *comp,
                                   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,
+                               buf, BMP280_COMP_TEMP_REG_COUNT);
+        if (ret < 0) {
+                dev_err(&data->client->dev,
+                        "failed to read temperature calibration parameters\n");
+                return ret;
+        }
 
-        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;
+        /*
+         * 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.
+         *
+         * Conversely, T1 and P1 are unsigned values, so they can be
+         * cast straight to the larger type.
+         */
+        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];
+
+        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) 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;
+        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;