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

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

[Beomho Seo]

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@samsung.com>
---
 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;
 }
-- 
1.7.9.5


-- 
Best Regards,

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

[Jonathan Cameron]

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@samsung.com>
Applied to the fixes-togreg branch of iio.git

Thanks,
> ---
>   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;
>   }
>

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

[Jonathan Cameron]

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@samsung.com>
> 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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