Re: [PATCH v6 2/2] iio: light: isl76682: Add ISL76682 driver

[Marek Vasut <marex@denx.de>]

On 12/4/23 12:29, Jonathan Cameron wrote:
> On Mon, 27 Nov 2023 22:26:53 +0100
> Marek Vasut <marex@denx.de> wrote:
> 
>> The ISL76682 is very basic ALS which only supports ALS or IR mode
>> in four ranges, 1k/4k/16k/64k LUX. There is no IRQ support or any
>> other fancy functionality.
>>
>> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>> Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
>> Signed-off-by: Marek Vasut <marex@denx.de>
> 
> There is a additional question on what scale means for
> an IR channel.  There aren't any well defined units (as it depends
> on the sensitivity curve) so in general we avoid providing scale
> for intensity readings.
> 
> The datasheet has a vague go at working around this problem by
> using counts relative to IR measurement in daylight which would
> measure 210 LUX.  (via faking that with a 850nm green led??)
> 
> That's far from a standard..
> 
> We do have precedence of scale applied to intensity channels
> so I guess the ship has sailed.
> 
> Perhaps we should just add an explicit not to the ABI docs
> to cover that changing the scale in these sensors will result
> in the counts changing, but multiplying raw by scale isn't going
> to give any sensible units.
> 
> So probably not a thing to fix in this series, but to address
> separately.

Is something like this what you have in mind ?

diff --git a/Documentation/ABI/testing/sysfs-bus-iio 
b/Documentation/ABI/testing/sysfs-bus-iio
index 0eadc08c3a139..584607f560d02 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -618,7 +618,9 @@ KernelVersion:      2.6.35
  Contact:       linux-iio@vger.kernel.org
  Description:
                 If a discrete set of scale values is available, they
-               are listed in this attribute.
+               are listed in this attribute. Unlike illumination,
+               multiplying intensity by intensity_scale does not
+               yield value with any standardized unit .

  What:          /sys/bus/iio/devices/iio:deviceX/out_voltageY_hardwaregain
  What:          /sys/bus/iio/devices/iio:deviceX/in_intensity_hardwaregain