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authorGwendal Grignou <gwendal@chromium.org>2019-03-13 12:40:02 +0100
committerJonathan Cameron <Jonathan.Cameron@huawei.com>2019-03-16 16:08:55 +0000
commit3d02d7082e5823598090530c3988a35f69689943 (patch)
tree1ffcb16eb7ce2e3a5badc8dfa6e703ed980fc385
parent2e4b88f73966adead360e47621df0183586fac32 (diff)
downloadlinux-3d02d7082e5823598090530c3988a35f69689943.tar.bz2
iio: cros_ec: Fix the maths for gyro scale calculation
Calculation did not use IIO_DEGREE_TO_RAD and implemented a variant to avoid precision loss as we aim a nano value. The offset added to avoid rounding error, though, doesn't give us a close result to the expected value. E.g. For 1000dps, the result should be: (1000 * pi ) / 180 >> 15 ~= 0.000532632218 But with current calculation we get $ cat scale 0.000547890 Fix the calculation by just doing the maths involved for a nano value val * pi * 10e12 / (180 * 2^15) so we get a closer result. $ cat scale 0.000532632 Fixes: c14dca07a31d ("iio: cros_ec_sensors: add ChromeOS EC Contiguous Sensors driver") Signed-off-by: Gwendal Grignou <gwendal@chromium.org> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com> Cc: <Stable@vger.kernel.org> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
-rw-r--r--drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
index 89cb0066a6e0..8d76afb87d87 100644
--- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
+++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
@@ -103,9 +103,10 @@ static int cros_ec_sensors_read(struct iio_dev *indio_dev,
* Do not use IIO_DEGREE_TO_RAD to avoid precision
* loss. Round to the nearest integer.
*/
- *val = div_s64(val64 * 314159 + 9000000ULL, 1000);
- *val2 = 18000 << (CROS_EC_SENSOR_BITS - 1);
- ret = IIO_VAL_FRACTIONAL;
+ *val = 0;
+ *val2 = div_s64(val64 * 3141592653ULL,
+ 180 << (CROS_EC_SENSOR_BITS - 1));
+ ret = IIO_VAL_INT_PLUS_NANO;
break;
case MOTIONSENSE_TYPE_MAG:
/*