linux-kernel - Re: [PATCH v3 1/2] leds: ncp5623: Add device tree binding documentation

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Message-ID: <20160928105858.GA24545@amd>
Date:   Wed, 28 Sep 2016 12:58:58 +0200
From:   Pavel Machek <pavel@....cz>
To:     Florian Vaussard <florian.vaussard@...il.com>
Cc:     devicetree@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <j.anaszewski@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        Florian Vaussard <florian.vaussard@...g-vd.ch>
Subject: Re: [PATCH v3 1/2] leds: ncp5623: Add device tree binding
 documentation

On Wed 2016-09-28 12:02:41, Florian Vaussard wrote:
> Hi Pavel,
> 
> Le 24. 09. 16 à 13:58, Pavel Machek a écrit :
> > Hi!
> > 
> >> +Example
> >> +=======
> >> +
> >> +led1: ncp5623@38 {
> >> +	#address-cells = <1>;
> >> +	#size-cells = <0>;
> >> +	compatible = "onnn,ncp5623";
> >> +	reg = <0x38>;
> >> +	onnn,led-iref-microamp = <10>;
> >> +
> >> +	led1r@0 {
> >> +		label = "ncp:power:red";
> >> +		linux,default-trigger = "default-on";
> > ...
> >> +	led1b@1 {
> >> +		label = "ncp:power:blue";
> >> +		reg = <1>;
> > 
> > Actually... the three LEDs are packaged such as this is one colorful
> > light to the user, right? Some day we'll need to group them, so that
> > kernel can automatically tell this is one led, and probably add extra
> > attributes, such as values that produce white light.
> > 
> 
> Actually, it's up to the hardware designer to choose. On my board for instance,
> this chip is driving an RGB LED, but it can really drive three independent LEDs
> if you want.

Yup. And driving RGB LED is really a bit different from driving three
independent LEDs: you'd for example like to be able to set the RGB LED
to white, and you need to know relative intensities for that.

So it would be good to have hardware description that captures
difference between RGB LED and three LEDs.

(And then, we'll want pattern engine to drive that. One day :-) ).

> I agree that the RGB case is quite common nowadays and currently not very well
> managed by the LED subsystem. But I do not think that this is specific to this
> driver.

No, it is not.

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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