Re: [PATCH] [BUGFIX] iio: mlx96014: Replace offset sign

[Jonathan Cameron <jic23@kernel.org>]

On 05/07/15 19:03, Crt Mori wrote:
> Changed the offset to negative as usual equation is: (raw +
> offset)*scale and in this
> case offset should be negative (as we deduct 273.15 Kelvin to get temperature
> in Celsius).
> 
> Signed-off-by: Crt Mori <cmo@melexis.com>
> Acked-by: Peter Meerwald <pmeerw@pmeerw.net>
Please don't do such patches as inline replies.  The white space has
also bee eaten.  I have hand applied the patch to the fixes-togreg
branch of iio.git

Thanks,

Jonathan
> ---
>  drivers/iio/temperature/mlx90614.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/temperature/mlx90614.c
> b/drivers/iio/temperature/mlx90614.c
> index c8b6ac8..951a50f 100644
> --- a/drivers/iio/temperature/mlx90614.c
> +++ b/drivers/iio/temperature/mlx90614.c
> @@ -58,7 +58,7 @@ static int mlx90614_read_raw(struct iio_dev *indio_dev,
>   *val = ret;
>   return IIO_VAL_INT;
>   case IIO_CHAN_INFO_OFFSET:
> - *val = 13657;
> + *val = -13657;
>   *val2 = 500000;
>   return IIO_VAL_INT_PLUS_MICRO;
>   case IIO_CHAN_INFO_SCALE:
> 
> 
> 
> On 5 July 2015 at 14:51, Jonathan Cameron <jic23@kernel.org> wrote:
>> On 29/06/15 15:43, Crt Mori wrote:
>>>>> Translates the magic constant numbers to named macros and add some
>>>>> additional comments about their meaning. Also changed the offset to
>>>>> negative as usual equation is: (raw + offset)*scale and in this
>>>>> case offset should be negative (as we deduct 273.15 Kelvin to get
>>>>> temperature in Celsius)..
>>>
>>>> On 29 June 2015 at 14:19, Peter Meerwald <pmeerw@pmeerw.net> wrote:
>>>> looks good; strictly, this patch is
>>>> (a) a bugfix (the offset should be negative),
>>>> (b) cleanup to replace constants by macros.
>>>
>>> I agree, but other things are more design than a proper change.
>> True, but the fix may well go via a faster route and be backported
>> to older kernels.  The other stuff is good, but we can take our time
>> with it.  Please split the patch and repost.
>>>
>>> I would also like you to reconsider the usage of
>>> IIO_CHAN_INFO_PROCESSED which would report calculated value
>>> to avoid knowing the sensor specifics and just provide general output
>>> (this would avoid different calculations of final temperature for different
>>> sensors).
>> If it can't be done via a straight linear map, then processed is the
>> only option.  If it can then it really doesn't matter as generic
>> userspace will handle it just fine.
>>>
>>>>>
>>>>> The diff is made towards togreg branch as that branch seems to have the
>>>>> most recent updates of mlx90614 driver (many are yet to be merged).
>>>>>
>>>>> Signed-off-by: Crt Mori <cmo@melexis.com>
>>>>> ---
>>>>>  drivers/iio/temperature/mlx90614.c | 20 ++++++++++++++------
>>>>>  1 file changed, 14 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/iio/temperature/mlx90614.c
>>>>> b/drivers/iio/temperature/mlx90614.c
>>>>> index cb2e8ad..909278a 100644
>>>>> --- a/drivers/iio/temperature/mlx90614.c
>>>>> +++ b/drivers/iio/temperature/mlx90614.c
>>>>> @@ -65,6 +65,13 @@
>>>>>
>>>>>  #define MLX90614_AUTOSLEEP_DELAY 5000 /* default autosleep delay */
>>>>>
>>>>> +/* Magic constants */
>>>>> +#define MLX90614_CONST_OFFSET_DEC -13657 /* decimal part of the Kelvin
>>>>> offset */
>>>>> +#define MLX90614_CONST_OFFSET_REM 500000 /* remainder of offset
>>>>> (273.15*50) */
>>>>> +#define MLX90614_CONST_SCALE 20 /* Scale in milliKelvin (0.02 * 1000) */
>>>>> +#define MLX90614_CONST_RAW_EMISSIVITY_MAX 65535 /* max value for
>>>>> emissivity */
>>>>> +#define MLX90614_CONST_EMISSIVITY_RESOLUTION 15259 /* 1/65535 ~
>>>>> 0.000015259 */
>>>>> +
>>>>>  struct mlx90614_data {
>>>>>         struct i2c_client *client;
>>>>>         struct mutex lock; /* for EEPROM access only */
>>>>> @@ -204,11 +211,11 @@ static int mlx90614_read_raw(struct iio_dev
>>>>> *indio_dev,
>>>>>                 *val = ret;
>>>>>                 return IIO_VAL_INT;
>>>>>         case IIO_CHAN_INFO_OFFSET:
>>>>> -               *val = 13657;
>>>>> -               *val2 = 500000;
>>>>> +               *val = MLX90614_CONST_OFFSET_DEC;
>>>>> +               *val2 = MLX90614_CONST_OFFSET_REM;
>>>>>                 return IIO_VAL_INT_PLUS_MICRO;
>>>>>         case IIO_CHAN_INFO_SCALE:
>>>>> -               *val = 20;
>>>>> +               *val = MLX90614_CONST_SCALE;
>>>>>                 return IIO_VAL_INT;
>>>>>         case IIO_CHAN_INFO_CALIBEMISSIVITY: /* 1/65535 / LSB */
>>>>>                 mlx90614_power_get(data, false);
>>>>> @@ -221,12 +228,12 @@ static int mlx90614_read_raw(struct iio_dev
>>>>> *indio_dev,
>>>>>                 if (ret < 0)
>>>>>                         return ret;
>>>>>
>>>>> -               if (ret == 65535) {
>>>>> +               if (ret == MLX90614_CONST_RAW_EMISSIVITY_MAX) {
>>>>>                         *val = 1;
>>>>>                         *val2 = 0;
>>>>>                 } else {
>>>>>                         *val = 0;
>>>>> -                       *val2 = ret * 15259; /* 1/65535 ~ 0.000015259 */
>>>>> +                       *val2 = ret * MLX90614_CONST_EMISSIVITY_RESOLUTION;
>>>>>                 }
>>>>>                 return IIO_VAL_INT_PLUS_NANO;
>>>>>         default:
>>>>> @@ -245,7 +252,8 @@ static int mlx90614_write_raw(struct iio_dev *indio_dev,
>>>>>         case IIO_CHAN_INFO_CALIBEMISSIVITY: /* 1/65535 / LSB */
>>>>>                 if (val < 0 || val2 < 0 || val > 1 || (val == 1 && val2 !=
>>>>> 0))
>>>>>                         return -EINVAL;
>>>>> -               val = val * 65535 + val2 / 15259; /* 1/65535 ~ 0.000015259
>>>>> */
>>>>> +               val = val * MLX90614_CONST_RAW_EMISSIVITY_MAX +
>>>>> +                       val2 / MLX90614_CONST_EMISSIVITY_RESOLUTION;
>>>>>
>>>>>                 mlx90614_power_get(data, false);
>>>>>                 mutex_lock(&data->lock);
>>>>>
>>> --
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>>
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