linux-kernel - Re: [PATCH V3] led: Backlight trigger for led subsystem

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Message-ID: <20081007185846.GA6604@elf.ucw.cz>
Date:	Tue, 7 Oct 2008 20:58:46 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Rodolfo Giometti <giometti@...eenne.com>
Cc:	linux-kernel@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>
Subject: Re: [PATCH V3] led: Backlight trigger for led subsystem

On Tue 2008-10-07 17:20:32, Rodolfo Giometti wrote:
> On Tue, Oct 07, 2008 at 03:54:20PM +0200, Pavel Machek wrote:
> > Hi!
> > 
> > > This patch set adds a new led trigger which emulates the backlight
> > > behaviour: the leds are turned off and on each time the display blanks
> > > and unblacks.
> > > 
> > > Since backlights are usually implemented with leds this patch set is
> > > useful for those drivers whose manage leds controller used as
> > > backlight controller.
> > > 
> > > The driver simply registers itself into the led subsystem and then the
> > > user may get backlight emulation by setting the "backlight"
> > > trigger. Moreover a driver, which usually manages more than one led,
> > > can use some leds as "led" and the others as "backlights" at user
> > > request.
> > 
> > We already have backlight subsystem, it can also handle display
> > brightness. Why not use that?
> 
> Just to use a led as "led" or as "backlight" at user request. You can
> do it by using:
> 
>    echo none > /sys/class/leds/lcd/trigger
>    echo backlight > /sys/class/leds/lcd/trigger
> 
> and the led will work accordingly.
> 
> Also a led used as "backlight" is just a normal led (you can set the
> brightness as a normal led) but it switchs off automatically when the
> LCD blanks.

Ok, what is it good for? So I have backlight, charging led and hdd led
on my zaurus. Now I can set charging led to indicate backlight... but
why is it useful?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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