linux-kernel - Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light Sensor

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Date:   Mon, 6 Nov 2023 14:10:43 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Subhajit Ghosh <subhajit.ghosh@...aklogic.com>,
        Jonathan Cameron <jic23@...nel.org>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Paul Gazzillo <paul@...zz.com>,
        Matt Ranostay <matt@...ostay.sg>,
        Stefan Windfeldt-Prytz <stefan.windfeldt-prytz@...s.com>,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light Sensor

On 11/6/23 14:04, Subhajit Ghosh wrote:
> On 6/11/23 21:43, Jonathan Cameron wrote:
>> On Tue, 31 Oct 2023 19:08:08 +1030
>> Subhajit Ghosh <subhajit.ghosh@...aklogic.com> wrote:
>>
>>>> Scale on the intensity channel is interesting...  What are the units?
>>>> There tend not to be any well defined units for intensity (as opposed
>>>> to illuminance).  There may be gain on the signal, but it won't be 
>>>> in untils
>>>> that map directly to a scale userspace should apply.  This is one of 
>>>> the
>>>> rare reasons for using the HARDWARE_GAIN element of the ABI.
>>>>
>>>> A tricky corner however as relationship between raw value and 
>>>> hardwaregain
>>>> is not tightly defined (as it can be really weird!)
>>> Hi Jonathan,
>>>
>>> Thank you for taking time for reviewing and clearing all my tiny 
>>> doubts and
>>> queries especially for the dt and versioning part. Much appreciated.
>>>
>>> In the above case, should I not expose scale for the "clear" channel? 
>>> Rather,
>>> how should I expose the "clear" channel to userspace?
>> What is the scale?  What units to you get after applying it?
> The scale is in Lux. The output after applying is Lux.

Hi Subhajit,

I am by no means an expert here but maybe you could check if the channel 
should be of type 'illuminance'? (To me 'Lux' sounds like an unit of 
illuminance rather than intensity).

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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