| Message ID | 20190313114002.11236-1-enric.balletbo@collabora.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] iio: cros_ec: Fix the maths for gyro scale calculation | expand |
On Wed, 13 Mar 2019 12:40:02 +0100 Enric Balletbo i Serra <enric.balletbo@collabora.com> wrote: > From: Gwendal Grignou <gwendal@chromium.org> > > 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> Applied to the fixes-togreg branch of iio.git and marked for stable. Thanks, Jonathan > --- > > Changes in v3: > - Fix 'warning: this decimal constant is unsigned only in ISO C90' spotted by kbuild test robot. > > 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..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: > /*
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: /*