linux-kernel - Re: RGB LED class Re: [PATCH v2 2/2] leds: lp50xx: Add the LP50XX family of the RGB LED driver

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Date:   Tue, 29 Jan 2019 00:04:08 +0100
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Dan Murphy <dmurphy@...com>, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        dachaac@...il.com, robh+dt@...nel.org
Subject: Re: RGB LED class Re: [PATCH v2 2/2] leds: lp50xx: Add the LP50XX
 family of the RGB LED driver

Hi!

> >>What algorithm would be used for mapping brightness levels to RGB values
> >>in case of devices without hardware support for that?
> >
> >Output power = brightness / max_brightness * pwm_channel[x].
> 
> IIUC you mean it as a formula for calculating r,g,b, values?
> I.e., on brightness setting we would have to do this calculation for
> each of three channels?
> 
> Then, it will result in changing hue as well. That's why we're
> discussing HSV.

It should not change the hue, AFAICT, modulo the rounding errors.

> >>s/pwm/color/
> >
> >s/pwm/power/ would work for me.
> 
> Power implies physical units. I'd prefer "intensity".

Intensity would work for me, too.

> >>Besides white also other color presets could be defined in DT.
> >
> >They should not be neccessary. When userspace knows what is white and
> >that power is linear with values in power_channels, it should be able
> >to do colorspace conversion itself.
> 
> Have you verified it in practice? Would it allow to convert RGB values
> of the color displayed on the monitor to LED RGB class intensities,
> allowing to achieve similar color on the LED?

Yes, I think so.

My code is in unicsy_demo repository, in monitor/notint.py .


									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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