On 05/06/15 12:03, Daniel Baluta wrote:
> The current computation for fractional part of the magnetic
> field is broken. This patch fixes it by taking a different
> approach. We expose the raw reading in milli Gauss (to avoid
> rounding errors) with a scale of 0.001.
>
> Thus the final computation is done in userspace where floating
> point operation are more relaxed.
>
> Fixes: abeb6b1e7b ("iio: magnetometer: Add support for MEMSIC MMC35240")
> Signed-off-by: Daniel Baluta <daniel.baluta@xxxxxxxxx>
Applied to the togreg branch of iio.git.
Thanks
> ---
> drivers/iio/magnetometer/mmc35240.c | 43 +++++++++++++++++++++++--------------
> 1 file changed, 27 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/iio/magnetometer/mmc35240.c b/drivers/iio/magnetometer/mmc35240.c
> index 9d62c53..7fff38e 100644
> --- a/drivers/iio/magnetometer/mmc35240.c
> +++ b/drivers/iio/magnetometer/mmc35240.c
> @@ -113,8 +113,9 @@ static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("100 200 333 666");
> .modified = 1, \
> .channel2 = IIO_MOD_ ## _axis, \
> .address = AXIS_ ## _axis, \
> - .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), \
> - .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SAMP_FREQ), \
> + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
> + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SAMP_FREQ) | \
> + BIT(IIO_CHAN_INFO_SCALE), \
> }
>
> static const struct iio_chan_spec mmc35240_channels[] = {
> @@ -241,9 +242,19 @@ static int mmc35240_read_measurement(struct mmc35240_data *data, __le16 buf[3])
> 3 * sizeof(__le16));
> }
>
> -static int mmc35240_raw_to_gauss(struct mmc35240_data *data, int index,
> - __le16 buf[],
> - int *val, int *val2)
> +/**
> + * mmc35240_raw_to_mgauss - convert raw readings to milli gauss. Also apply
> + compensation for output value.
> + *
> + * @data: device private data
> + * @index: axis index for which we want the conversion
> + * @buf: raw data to be converted, 2 bytes in little endian format
> + * @val: compensated output reading (unit is milli gauss)
> + *
> + * Returns: 0 in case of success, -EINVAL when @index is not valid
> + */
> +static int mmc35240_raw_to_mgauss(struct mmc35240_data *data, int index,
> + __le16 buf[], int *val)
> {
> int raw_x, raw_y, raw_z;
> int sens_x, sens_y, sens_z;
> @@ -261,18 +272,15 @@ static int mmc35240_raw_to_gauss(struct mmc35240_data *data, int index,
>
> switch (index) {
> case AXIS_X:
> - *val = (raw_x - nfo) / sens_x;
> - *val2 = ((raw_x - nfo) % sens_x) * 1000000;
> + *val = (raw_x - nfo) * 1000 / sens_x;
> break;
> case AXIS_Y:
> - *val = (raw_y - nfo) / sens_y - (raw_z - nfo) / sens_z;
> - *val2 = (((raw_y - nfo) % sens_y - (raw_z - nfo) % sens_z))
> - * 1000000;
> + *val = (raw_y - nfo) * 1000 / sens_y -
> + (raw_z - nfo) * 1000 / sens_z;
> break;
> case AXIS_Z:
> - *val = (raw_y - nfo) / sens_y + (raw_z - nfo) / sens_z;
> - *val2 = (((raw_y - nfo) % sens_y + (raw_z - nfo) % sens_z))
> - * 1000000;
> + *val = (raw_y - nfo) * 1000 / sens_y +
> + (raw_z - nfo) * 1000 / sens_z;
> break;
> default:
> return -EINVAL;
> @@ -290,16 +298,19 @@ static int mmc35240_read_raw(struct iio_dev *indio_dev,
> __le16 buf[3];
>
> switch (mask) {
> - case IIO_CHAN_INFO_PROCESSED:
> + case IIO_CHAN_INFO_RAW:
> mutex_lock(&data->mutex);
> ret = mmc35240_read_measurement(data, buf);
> mutex_unlock(&data->mutex);
> if (ret < 0)
> return ret;
> - ret = mmc35240_raw_to_gauss(data, chan->address,
> - buf, val, val2);
> + ret = mmc35240_raw_to_mgauss(data, chan->address, buf, val);
> if (ret < 0)
> return ret;
> + return IIO_VAL_INT;
> + case IIO_CHAN_INFO_SCALE:
> + *val = 0;
> + *val2 = 1000;
> return IIO_VAL_INT_PLUS_MICRO;
> case IIO_CHAN_INFO_SAMP_FREQ:
> mutex_lock(&data->mutex);
>
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