Re: [PATCH 01/15] iio: adc: ad4030: Fix _scale for when oversampling is enabled

[David Lechner <dlechner@baylibre.com>]

On 8/30/25 1:43 PM, Jonathan Cameron wrote:
> On Fri, 29 Aug 2025 21:40:24 -0300
> Marcelo Schmitt <marcelo.schmitt@analog.com> wrote:
> 
>> Previously, the AD4030 driver was using the number of scan realbits for the
>> voltage channel to derive the scale to millivolts. Though, when sample
>> averaging is enabled (oversampling_ratio > 1), the number of scan realbits
>> for the channel is set to 30 and doesn't match the amount of conversion
>> precision bits. Due to that, the calculated channel scale did not correctly
>> scale raw sample data to millivolt units in those cases. Use chip specific
>> precision bits to derive the correct channel _scale on every and all
>> channel configuration.
>>
>> Fixes: dc78e71d7c15 ("iio: adc: ad4030: remove some duplicate code")
>> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
> 
> Hi Marcelo
> 
> I was assuming that when this said 'averaging' it actually meant
> summing (there is a note about using the upper precision bits to get the same
> scaling which is what we'd expect it were simply summing over X samples).
> 
> So given that we don't divide back down to get the original scaling I'm
> not following how this works.

I had the same feeling. I have some hardware I can test later this week.