This is a note to let you know that I've just added the patch titled

iio: cros_ec: Fix the maths for gyro scale calculation

to my staging git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git in the staging-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 3d02d7082e5823598090530c3988a35f69689943 Mon Sep 17 00:00:00 2001

From: Gwendal Grignou gwendal@chromium.org Date: Wed, 13 Mar 2019 12:40:02 +0100 Subject: 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 --- 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: /*