iio: ak8975: Fix calculation formula for convert micro tesla to gauss unit

Oen micro tesla equal 0.01 gauss. So I have fixed calculation formula And add RAW_TO_GAUSS macro.
ASA is in the range of 0 to 255. If multiply 0.003, calculation result(in_magn_[*]_scale) is
always 0. So multiply 3000 and return IIO_VAL_INT_PLUS_MICRO.
As a result read_raw call back function return accurate scale value.

Change-Id: Ia00b801d4867955eef661b64add82ca634f0256c
Signed-off-by: Beomho Seo <beomho.seo@samsung.com>

diff --git a/drivers/iio/magnetometer/ak8975.c b/drivers/iio/magnetometer/ak8975.c
index d46f10b..aeba3bb 100644 (file)
--- a/drivers/iio/magnetometer/ak8975.c
+++ b/drivers/iio/magnetometer/ak8975.c
@@ -85,6 +85,7 @@
 #define AK8975_MAX_CONVERSION_TIMEOUT  500
 #define AK8975_CONVERSION_DONE_POLL_TIME 10
 #define AK8975_DATA_READY_TIMEOUT      ((100*HZ)/1000)
+#define RAW_TO_GAUSS(asa) ((((asa) + 128) * 3000) / 256)
 
 /*
  * Per-instance context data for the device.
@@ -265,15 +266,15 @@ static int ak8975_setup(struct i2c_client *client)
  *
  * Since 1uT = 100 gauss, our final scale factor becomes:
  *
- * Hadj = H * ((ASA + 128) / 256) * 3/10 * 100
- * Hadj = H * ((ASA + 128) * 30 / 256
+ * Hadj = H * ((ASA + 128) / 256) * 3/10 * 1/100
+ * Hadj = H * ((ASA + 128) * 0.003) / 256
  *
  * Since ASA doesn't change, we cache the resultant scale factor into the
  * device context in ak8975_setup().
  */
-       data->raw_to_gauss[0] = ((data->asa[0] + 128) * 30) >> 8;
-       data->raw_to_gauss[1] = ((data->asa[1] + 128) * 30) >> 8;
-       data->raw_to_gauss[2] = ((data->asa[2] + 128) * 30) >> 8;
+       data->raw_to_gauss[0] = RAW_TO_GAUSS(data->asa[0]);
+       data->raw_to_gauss[1] = RAW_TO_GAUSS(data->asa[1]);
+       data->raw_to_gauss[2] = RAW_TO_GAUSS(data->asa[2]);
 
        return 0;
 }
@@ -421,8 +422,9 @@ static int ak8975_read_raw(struct iio_dev *indio_dev,
        case IIO_CHAN_INFO_RAW:
                return ak8975_read_axis(indio_dev, chan->address, val);
        case IIO_CHAN_INFO_SCALE:
-               *val = data->raw_to_gauss[chan->address];
-               return IIO_VAL_INT;
+               *val = 0;
+               *val2 = data->raw_to_gauss[chan->address];
+               return IIO_VAL_INT_PLUS_MICRO;
        }
        return -EINVAL;
 }