releases/4.19.37/iio-cros_ec-fix-the-maths-for-gyro-scale-calculation.patch

   1 From 3d02d7082e5823598090530c3988a35f69689943 Mon Sep 17 00:00:00 2001
   2 From: Gwendal Grignou <gwendal@chromium.org>
   3 Date: Wed, 13 Mar 2019 12:40:02 +0100
   4 Subject: iio: cros_ec: Fix the maths for gyro scale calculation
   5
   6 From: Gwendal Grignou <gwendal@chromium.org>
   7
   8 commit 3d02d7082e5823598090530c3988a35f69689943 upstream.
   9
  10 Calculation did not use IIO_DEGREE_TO_RAD and implemented a variant to
  11 avoid precision loss as we aim a nano value. The offset added to avoid
  12 rounding error, though, doesn't give us a close result to the expected
  13 value. E.g.
  14
  15 For 1000dps, the result should be:
  16
  17     (1000 * pi ) / 180 >> 15 ~= 0.000532632218
  18
  19 But with current calculation we get
  20
  21     $ cat scale
  22     0.000547890
  23
  24 Fix the calculation by just doing the maths involved for a nano value
  25
  26    val * pi * 10e12 / (180 * 2^15)
  27
  28 so we get a closer result.
  29
  30     $ cat scale
  31     0.000532632
  32
  33 Fixes: c14dca07a31d ("iio: cros_ec_sensors: add ChromeOS EC Contiguous Sensors driver")
  34 Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
  35 Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
  36 Cc: <Stable@vger.kernel.org>
  37 Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
  38 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  39
  40 ---
  41  drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c |    7 ++++---
  42  1 file changed, 4 insertions(+), 3 deletions(-)
  43
  44 --- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
  45 +++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
  46 @@ -103,9 +103,10 @@ static int cros_ec_sensors_read(struct i
  47                          * Do not use IIO_DEGREE_TO_RAD to avoid precision
  48                          * loss. Round to the nearest integer.
  49                          */
  50 -                       *val = div_s64(val64 * 314159 + 9000000ULL, 1000);
  51 -                       *val2 = 18000 << (CROS_EC_SENSOR_BITS - 1);
  52 -                       ret = IIO_VAL_FRACTIONAL;
  53 +                       *val = 0;
  54 +                       *val2 = div_s64(val64 * 3141592653ULL,
  55 +                                       180 << (CROS_EC_SENSOR_BITS - 1));
  56 +                       ret = IIO_VAL_INT_PLUS_NANO;
  57                         break;
  58                 case MOTIONSENSE_TYPE_MAG:
  59                         /*