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

[Jacek Anaszewski]

Hi Heiner,

On 03/30/2016 03:59 PM, Heiner Kallweit wrote:
> On Wed, Mar 30, 2016 at 3:03 PM, Pavel Machek <pavel@xxxxxx> wrote:
> > 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".
>
> That's a good example. As long as you can recognize green+orange as
> separate lights/colors
> (w/o magnifying glass) I wouldn't call it "a LED with multiple colors"
> but "multiple
> LED devices".
>
> In my use case we talk about RGB LEDs like the commonly used 5050 SMD RGB LEDs.
> And it's not only about using a handful of discrete colors but about
> displaying any arbitrary
> color.
> So far the kernel exposes the physical RGB LEDs as separate LEDs only
> and I can't use
> a trigger to e.g. set "magenta with 50% brightness".

I think that we should consult more people before pushing the solution
upstream. Would you mind writing a message with an explanation of the
issue to linux-api list?

Please keep in mind also the information from the "Attributes" section
of Documentation/filesystems/sysfs.txt.

--
Best regards,
Jacek Anaszewski