iio: magnetometer: mmc35240: Fix broken processed value

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@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/iio/magnetometer/mmc35240.c b/drivers/iio/magnetometer/mmc35240.c
index 78da0d1..146ae66 100644 (file)
--- 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);