linux-kernel - Re: [PATCH 2/2] leds: lp5024: Add the LP5024/18 RGB LED driver

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Date:   Wed, 19 Dec 2018 23:27:37 +0100
From:   Pavel Machek <pavel@....cz>
To:     Dan Murphy <dmurphy@...com>
Cc:     jacek.anaszewski@...il.com, linux-leds@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] leds: lp5024: Add the LP5024/18 RGB LED driver

Hi!

[cc list trimmed]

> >>> I don't think a user needs nor would want to have 24 different LED nodes with 24 different brightness files.
> >>> Or with the LP5036 that would have 36 LED nodes.
> >>>
> >>> Table 1 in the data sheet shows how the outputs map to the control banks to the LED registers.
> >>
> >> Some time ago we had discussion with Vesa Jääskeläinen about possible
> >> approaches to RGB LEDs [0]. What seemed to be the most suitable
> >> variation of the discussed out-of-tree approach was the "color" property
> >> and array of color triplets defined in Device Tree per each color.
> >>
> >> Please refer to [0] for the details.
> >>
> >> [0] https://lkml.org/lkml/2018/11/9/938
> > 
> > Yes, plus I also have the set of HSV patches somewhere... and they
> > work, but I found out that HSV->RGB conversion results in loss of precision.
> > 
> > We may want to do something like that.
> > 
> > But we need to do it once, in a driver core. We obviously don't want
> > each driver having different version of RGB support.
> 
> True.  But the RGB driver really should not be defining the color palette.
> 
> Maybe a "color capability" reported to user space so that the user space can make the decision.
> 
> It can report
> 
> For GPIO or constant current situations
> static red
> static blue
> static green 
> 
> For adjustable configurations it can report:
> variable red
> variable blue
> variable green
> 
> or even simpler "static" or "dynamic" as a return to report the RGB configuration.
> The LED driver would just need to set the variable.

I'm not sure what static/variable is.

I have RGB leds here that can set any channel to 0-255, at
runtime. They seem to be quite common at phones.

Anyway, if your 36 channels can be set independently, I believe you
just want them to export as 36 LEDs.

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

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