linux-kernel - Re: [PATCH 3/3] arm64: dts: qcom: sm7225-fairphone-fp4: configure flash LED

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Message-Id: <CRKG1O4FKEAM.1629YG20LFZBN@otso>
Date:   Fri, 31 Mar 2023 10:59:51 +0200
From:   "Luca Weiss" <luca.weiss@...rphone.com>
To:     "Pavel Machek" <pavel@....cz>,
        "Fenglin Wu" <quic_fenglinw@...cinc.com>
Cc:     "Andy Gross" <agross@...nel.org>,
        "Bjorn Andersson" <andersson@...nel.org>,
        "Konrad Dybcio" <konrad.dybcio@...aro.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-leds@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] arm64: dts: qcom: sm7225-fairphone-fp4: configure
 flash LED

Hi Pavel,

On Thu Mar 23, 2023 at 8:54 PM CET, Pavel Machek wrote:
> Hi!
>
>
> > > > I'm pretty sure the flash is not yellow.
> > > 
> > > The marketing term is Dual LED flash or Dual-tone flash, one LED is a
> > > blue-ish white and one is a yellow-ish white, but from what I can tell,
> > > in the original code it's always referred to as white and yellow so I
> > > also followed that here.
> > > 
> > > Also the LEDs are right next to each other so in practise for torch just
> > > both go on, and for camera flash I cannot really tell you but I guess
> > > it's doing something there with the camera tuning.
> > > 
> > > See also this picture:
> > > https://shop.fairphone.com/media/catalog/product/cache/b752d78484639b19641a8560800d919d/p/_/p_5b_main_camera_back.jpg
> > > 
> > Hi Pavel,
> > 
> > Luca is right. It is normally called dual CCT (Correlated Color Temperature)
> > flash LED. It has 2 LEDs, one is with higher CCT (~6000K) so it looks like a
> > white LED, another is with lower CCT (~2000K) and it looks like a yellow
> > LED. I am not an expert of this but my understanding is the camera tuning
> > process normally adjusts the brightness of the two LEDs and enables them to
> > get different CCT for different snapshots.
>
> I believe this is normally called "warm white" and "cool white", no?
> Yellow would be monochromatic light at cca 575nm, see
> https://en.wikipedia.org/wiki/Shades_of_yellow .

I don't really have any more information I can provide right now. If you
feel it should be called warm white and cool white, feel free to send a
patch changing it.

I'm personally okay with it being called white & yellow since that seems
to be the term used in (downstream) software for these kinds of leds.

Regards
Luca

>
> If we need to add some defines for that, lets do that.
>
> BR,
> 									Pavel
> -- 
> People of Russia, stop Putin before his war on Ukraine escalates.