Re: We have multicolor, but should we turn it into RGB?

From: Pavel Machek <pavel@ucw.cz>
To: "Marek Behún" <marek.behun@nic.cz>
Cc: jacek.anaszewski@gmail.com, dmurphy@ti.com, linux-leds@vger.kernel.org
Subject: Re: We have multicolor, but should we turn it into RGB?
Date: Mon, 27 Jul 2020 12:20:58 +0200	[thread overview]
Message-ID: <20200727102058.GA16553@amd> (raw)
In-Reply-To: <20200727114048.32f36c59@dellmb.labs.office.nic.cz>

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Hi!

> > Multicolor is a bit too abstract. Yes, we can have
> > Green-Magenta-Ultraviolet LED, but so far all the LEDs we support are
> > RGB, and not even RGB-White or RGB-Yellow variants emerged.
> > 
> > Multicolor is not a good fit for RGB LED. It does not really know
> > about LED color.  In particular, there's no way to make LED "white".
> > 
> > Userspace is interested in knowing "this LED can produce arbitrary
> > color", which not all multicolor LEDs can.
> > 
> > 	Proposal: let's add "rgb" to led_colors in
> > 	drivers/leds/led-core.c, add corresponding device tree
> > 	defines, and use that, instead of multicolor for RGB LEDs.
> > 
> > 	We really need to do that now; "white" stuff can wait.
> > 
> > RGB LEDs are quite common, and it would be good to be able to turn LED
> > white and to turn it into any arbitrary color. It is essential that
> > userspace is able to set arbitrary colors, and it might be good to
> > have that ability from kernel, too... to allow full-color triggers.
> 
> I am not against adding RGB if you want to somehow teach the subsystem
> to mix arbitrary color (either by teaching it color curves or some
> other way). But I think we shouldn't remove multicolor, and here's the
> reason why:

I'd not remove multicolor. It would be still there for non-RGB
uses. (Sorry if I was unclear).

But I may want to disable it for now, not to have ABI incompatibility
in future.

> Most of the time I have seen 2 LEDs per ethernet port, green and yellow,
> but some ports have 2 Bi-Color LEDs, each consisting of green and
> yellow. I think most of the time these are 2-terminal LEDs.
> 
> So basically here we have, instead of a RGB LED, a GY LED (GY for
> green/yellow).
...
> So if we want to reasonably add support for this configuration of LEDs
> and to offer the user to configure these DUAL modes via the trigger
> API, I think these LEDs should be shown in the system as multicolor
> LEDs.

Yes, I guess multicolor may make sense there.

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

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