linux-kernel - Re: [PATCH v3 2/3] iio: light: ltr390: Add ALS channel and support for gain and resolution

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Message-ID: <CAG=0RqKuhn-WHjMbEqq4bCQOs9ERPKZR_udeCf3noqz+TzULyA@mail.gmail.com>
Date: Tue, 30 Jul 2024 12:47:10 +0530
From: Abhash jha <abhashkumarjha123@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: linux-iio@...r.kernel.org, anshulusr@...il.com, lars@...afoo.de, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] iio: light: ltr390: Add ALS channel and support
 for gain and resolution

On Tue, Jul 30, 2024 at 1:23 AM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Mon, 29 Jul 2024 17:20:54 +0530
> Abhash Jha <abhashkumarjha123@...il.com> wrote:
>
> > Add new ALS channel and allow reading raw and scale values.
> > Also provide gain and resolution configuration for ALS channel.
> > Add automatic mode switching between the UVS and ALS channel
> > based on which channel is being accessed.
> > The default mode in which the sensor start is ALS mode.
> >
> > Signed-off-by: Abhash Jha <abhashkumarjha123@...il.com>
> Hi Abhash,
>
> Patch looks good but one quick question.
> Why not present an IIO_LIGHT channel?  Needs to be converted
> to be illuminance (with scale / offset applied) rather than IIO_INTENSITY
> which we use when the frequency response is different from the requirements
> to measure Lux (and the units get very vague!)
>
> Looks like what you have here is close, but not quite the right scale
> factor as not including integration time and the mysterious 0.6 on the datasheet.

Yes, I just noticed it now. I will provide the integration time and
0.6 as part of the
scale calculation in the next version.

>
> If we can provide a signal scaled to illuminance that tends to be a lot
> more useful for things like screen brightness control because it should
> be close at least to other light sensors.
>
Hi Jonathan,
It did not occur to me that the IIO_LIGHT channel could be used
directly and hence I
went with the IIO_INTENSITY approach.
Yes we could provide the IIO_LIGHT channel and perform lux calculation
in the driver.
Would that mean forgoing the IIO_INTENSITY channel? Or do we keep both?

Abhash

> Jonathan