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

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Date:	Thu, 7 Apr 2016 22:45:40 +0200
From:	Pavel Machek <pavel@....cz>
To:	Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:	Jacek Anaszewski <j.anaszewski@...sung.com>,
	Heiner Kallweit <hkallweit1@...il.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,
	pali.rohar@...il.com, sre@...nel.org, khilman@...nel.org,
	aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
	Patrik Bachan <patrikbachan@...il.com>, serge@...lyn.com
Subject: Re: [PATCH v5 1/4] leds: core: add generic support for RGB Color
 LED's

Hi!

> >>The "color" attribute would contain "R G B" values. Setting the "color"
> >>attribute of any of the three LED class devices would affect brightness
> >>properties (i.e. constituent colors) of the remaining two ones.
> >>It would result in disabling any active triggers and writing all the
> >>three color settings to the RGB LED controller at one go.
> >
> >Having one attribute across three devices is rather ugly. And we'll
> >need to solve the pattern issue one day.
> >
> >What's tricky about patterns is that you need to control 3 (or more)
> >leds at a time. Problem you are trying to solve here is ... control of
> >3 leds, at the same time.
> >
> >So let's solve them together.
> 
> OK, now I've got your point. So we'd need to have a means for defining
> patterns. The interface could be located at /sys/class/leds/patterns.
> 
> We'd need to have a flexible way for defining LED class devices involved
> in a pattern. Since we cannot guarantee no space in a LED class device
> name, then a single attribute containing space separated list is not an
> option. We'd have to create a predefined set of attributes that would
> contain LED class device name. Predefined implies that it would be
> a fixed number, i.e. either some attributes would always remain unused
> or, which is even worse, we could run out of free attributes for some
> use cases.

There's a better solution: make pattern behave as a trigger for leds
it controls.

So we'd have

/sys/class/leds/patterns/lp5523

then we'd have

/sys/class/leds/lp5523::red/trigger = "lp5523:1"
/sys/class/leds/lp5523::green/trigger = "lp5523:2"
/sys/class/leds/lp5523::blue/trigger = "lp5523:3"

(or something similar, I'd have to boot the n900 to see the exact
names).

That means that we don't need space-separated lists. (And actually
gives us more flexibility; Maemo for example used the pattern engine
not for RGB led, but for 6 keyboard backlight leds.)

> The same constraints would appear if we wanted to be able to define
> more than one pattern.

We'd like to have more than one pattern _engine_, but it should be
enough to have one pattern per pattern engine at a time. 

> It would be best to work out more flexible solution. I wonder if
> ioctl interface isn't the only option.

Well, there's configs, which is more flexible, but...

Best regards,

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