linux-kernel - Re: [PATCH v5 1/4] leds: core: add generic support for RGB Color LED's

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Date:	Wed, 30 Mar 2016 15:03:19 +0200
From:	Pavel Machek <pavel@....cz>
To:	Jacek Anaszewski <j.anaszewski@...sung.com>
Cc:	Heiner Kallweit <hkallweit1@...il.com>, pali.rohar@...il.com,
	sre@...nel.org, khilman@...nel.org, aaro.koskinen@....fi,
	ivo.g.dimitrov.75@...il.com, patrikbachan@...il.com,
	serge@...lyn.com, Greg KH <greg@...ah.com>,
	linux-leds@...r.kernel.org,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v5 1/4] leds: core: add generic support for RGB Color
 LED's

Hi!

> >Ok, so:
> >
> >a) Do we want RGB leds to be handled by existing subsystem, or do we
> >need separate layer on top of that?
> >
> >b) Does RGB make sense, or HSV? RGB is quite widely used in graphics,
> >and it is what hardware implements. (But we'd need to do gamma
> >correction).
> >
> >c) My hardware has "acceleration engine", LED is independend from
> >CPU. That's rather big deal. Does yours? It seems to be quite common,
> >at least in cellphones.
> >
> >Ideally, I'd like to have "triggers", but different ones. As in: if
> >charging, do yellow " .xX" pattern. If fully charged, do green steady
> >light. If message is waiting, do blue " x x" pattern. If none of
> >above, do slow white blinking. (Plus priorities of events). But that's
> >quite different from existing support...)
> 
> Please note that HSV colour scheme allows to neatly project monochrome
> brightness semantics on the RGB realm. I.e. you can have fixed
> hue and saturation, and by changing the brightness component a perceived
> colour intensity can be altered.

I see HSV has some advantages. But we already have LEDs with multiple
colors, and kernel already handles them:

pavel@duo:~$ ls -1 /sys/class/leds/
tpacpi:green:batt
tpacpi:orange:batt

This is physically 2 leds but hidden under one indicator, so you got
"off", "green", "orange" and "green+orange".
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html