Re: [PATCH 4/4] staging: iio: light: isl29018: Use standard sysfs attributes for range and scale

[Roberta Dobrescu <roberta.dobrescu@gmail.com>]

On 08.03.2015 13:50, Jonathan Cameron wrote:
> On 23/02/15 19:35, Roberta Dobrescu wrote:
>> This patch refactors the isl29018 driver code in order to use standard
>> sysfs attributes for range and scale.
>>
>> ISL29018 light sensor uses four ranges and four ADC's resolutions
>> which influence the calculated lux.
>>
>> This patch eliminates the resolution (adc bits) and introduces scale.
>> Each range (1k, 4k, 16k or 64k) has a corresponding set of 4 scales
>> (for 16, 12, 8 or 4 bits). Both range and scale can be changed by the
>> user according to the corresponding set of values (exposed by the attributes
>> in_illuminance_range_available and in_illuminance_scale_available).
>>
>> When the range is changed, the set of available scales is set accordingly and
>> by default the scale used is the one for 16 adc bits. Scale can be changed
>> anytime with one of the available values.
> So we have 3 things interacting here.
>
> range - absolutely controlled for the device
> scale - from current range, with the adc resolution confusing things - we could just
>          multiply the output result up and not need to report this to userspace at all
> integration_time - This is the one element that's really being controlled by the adc
>                     resolution. This adc resolution is really effecting our sensitivity
>                     not the accuracy of measurement of the signal.
>
> Hence I'd have your adc resolution controlled by in_illuminance0_integration_time
> and the full scale range controlled by scale.
>
> For the lower adc resolutions simply apply the relevant scaling to get the output
> value to be on the same scale (assuming the range has not changed)
>
> How does that sound?

Sounds good :D.

Thanks for reviewing this.

Roberta