Re: [PATCH RESEND 1/2] iio: ak8975: Fix calculation formula for convert micro tesla to gauss unit

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On 08/02/14 10:25, Jonathan Cameron wrote:
On 04/02/14 09:15, Beomho Seo wrote:

One 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 and IIO_VAL_INT_PLUS_MICRO.
As a result, read_raw call back function return accurate scale value.

Signed-off-by: Beomho Seo <beomho.seo@xxxxxxxxxxx>
Applied to the fixes-togreg branch of iio.git

Thanks,
I forgot to mention that I added a line to the description on what the effect of the bug
was and also marked this for stable.

Thanks,

Jonathan
---
  drivers/iio/magnetometer/ak8975.c |   16 +++++++++-------
  1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/magnetometer/ak8975.c b/drivers/iio/magnetometer/ak8975.c
index ff284e5..0542354 100644
--- 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 = 0.01 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;
  }
@@ -428,8 +429,9 @@ 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;
  }


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