linux-kernel - Re: [Linux-fbdev-devel] 2.6.21-rc1 dims my LCD

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Message-Id: <1172510039.7101.3.camel@daplas>
Date:	Tue, 27 Feb 2007 01:13:59 +0800
From:	"Antonino A. Daplas" <adaplas@...il.com>
To:	linux-fbdev-devel@...ts.sourceforge.net
Cc:	Jiri Kosina <jikos@...os.cz>, linux-kernel@...r.kernel.org,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Richard Purdie <rpurdie@...ys.net>
Subject: Re: [Linux-fbdev-devel] 2.6.21-rc1 dims my LCD

On Mon, 2007-02-26 at 15:43 +0000, Richard Purdie wrote:
> On Mon, 2007-02-26 at 16:24 +0100, Jiri Kosina wrote:
> > On Mon, 26 Feb 2007, Richard Purdie wrote:
> > 
> > > Jiri: I've appended a patch that should already be queued, could you
> > > test and see if it solves the problem.
> > 
> > Thanks. In the meantime I have gone through the code and I can confirm 
> > that this is the root cause of what I am observing.
> > 
> > Now regarding the patch - at the time when the dim happened previously, 
> > currently there is a observable blink (after which the brightness is 
> > correct). 
> 
> The reason for the behaviour is that its turning the backlight down/off
> to save power as it thinks the screen is blank. The blink therefore
> makes sense as far as the backlight class is concerned and its working
> as intended now.
> 
> > I have put some debugging printk() into fb_notifier_callback(), 
> > and it turns out that on FB_EVENT_CONBLANK, there are two successive calls 
> > to backlight_update_status(), second immediately following the first one:
> > 
> > Feb 26 15:11:14 thunder kernel: calling backlight_update_status() with bd->props.fb_blank == 1, bd->props.brightness == 0
> > Feb 26 15:11:14 thunder kernel: calling backlight_update_status() with bd->props.fb_blank == 0, bd->props.brightness == 0
> > 
> > Is this really a right thing to do?

Well, no, the console should not blank and immediately unblank. Of
course, the console can blank after some time and can be induced to
unblank after a keyboard event, for example.

Besides the debugging printk's, can you also add something like
WARN_ON(1); so you can get a tracing too.

Tony


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