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

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Message-ID: <20081007152032.GH13035@tekkaman>
Date:	Tue, 7 Oct 2008 17:20:32 +0200
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	Pavel Machek <pavel@...e.cz>
Cc:	linux-kernel@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>
Subject: Re: [PATCH V3] led: Backlight trigger for led subsystem

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.

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
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