Re: [PATCH RFC] iio: adc: ad4030: fix calibscale read/write unit mismatch

[David Lechner <dlechner@baylibre.com>]

On 2/25/26 5:53 AM, Marcelo Schmitt wrote:
> On 02/25, Giorgi Tchankvetadze wrote:
>> The read path returns calibscale in IIO_VAL_INT_PLUS_NANO but the write
>> path treats it as MICRO. Since no write_raw_get_fmt is provided, the
>> IIO core defaults to MICRO when parsing userspace input.
>>
>> This means reading calibscale and writing it back results in a ~1000x
>> gain error.
>>
>> Change the read path and available range to use MICRO to match the
>> write path.
> 
> The updates to ad4030 driver will add write_raw_get_fmt() [1].
> [1]: https://lore.kernel.org/linux-iio/516cccc47e917bd26be29b016907f50a244a68b9.1771865684.git.marcelo.schmitt@analog.com/
> 
> At first glance, I think this could instead add a case to write_raw_get_fmt(),
> keeping calibscale nano precision (unless nano precision doesn't make sense
> for ad4030 calibscale (don't recall from top of my mind)).

Since this is a fix and needs to be backported, it probably make sense
to not depend on a patch that is adding new features.

I'm sure Jonathan will have an opinion about how he would like to handle
a conflict between the fixes and testing branches though.

> 
>>
>> Fixes: 0cb8b324852f ("iio: adc: ad4030: add driver for ad4030-24")
>> Signed-off-by: Giorgi Tchankvetadze <giorgitchankvetadze1997@gmail.com>
>> ---
>>  drivers/iio/adc/ad4030.c | 10 +++++-----
>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/iio/adc/ad4030.c b/drivers/iio/adc/ad4030.c
>> index def3e1d01ceb..3d823648371d 100644
>> --- a/drivers/iio/adc/ad4030.c
>> +++ b/drivers/iio/adc/ad4030.c
>> @@ -423,10 +423,10 @@ static int ad4030_get_chan_calibscale(struct iio_dev *indio_dev,
>>  
>>  	/* From datasheet: multiplied output = input × gain word/0x8000 */
>>  	*val = gain / AD4030_GAIN_MIDLE_POINT;
>> -	*val2 = mul_u64_u32_div(gain % AD4030_GAIN_MIDLE_POINT, NANO,
>> +	*val2 = mul_u64_u32_div(gain % AD4030_GAIN_MIDLE_POINT, MICRO,
>>  				AD4030_GAIN_MIDLE_POINT);
>>  
>> -	return IIO_VAL_INT_PLUS_NANO;
>> +	return IIO_VAL_INT_PLUS_MICRO;
>>  }
>>  
>>  /* Returns the offset where 1 LSB = (VREF/2^precision_bits - 1)/gain */
>> @@ -720,8 +720,8 @@ static irqreturn_t ad4030_trigger_handler(int irq, void *p)
>>  
>>  static const int ad4030_gain_avail[3][2] = {
>>  	{ 0, 0 },
>> -	{ 0, 30518 },
>> -	{ 1, 999969482 },
>> +	{ 0, 30 },
>> +	{ 1, 999969 },

This loses precision. Instead I would change the write to IIO_VAL_INT_PLUS_NANO
to match the read.

>>  };
>>  
>>  static int ad4030_read_avail(struct iio_dev *indio_dev,
>> @@ -739,7 +739,7 @@ static int ad4030_read_avail(struct iio_dev *indio_dev,
>>  
>>  	case IIO_CHAN_INFO_CALIBSCALE:
>>  		*vals = (void *)ad4030_gain_avail;
>> -		*type = IIO_VAL_INT_PLUS_NANO;
>> +		*type = IIO_VAL_INT_PLUS_MICRO;
>>  		return IIO_AVAIL_RANGE;
>>  
>>  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
>> -- 
>> 2.52.0
>>
>>