From: Gwendal Grignou <gwendal@xxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
---
Changes in v2:
- Do the maths instead of play with dividers as pointed by Jonathan.
drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c | 7 ++++---
1 file 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..401b22e08d48 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 * 3141592653,
+ 180 << (CROS_EC_SENSOR_BITS - 1));
+ ret = IIO_VAL_INT_PLUS_NANO;
break;
case MOTIONSENSE_TYPE_MAG:
/*
--
2.20.1
