Re: 2.6.21-rc1 dims my LCD

On Mon, 2007-02-26 at 16:24 +0100, Jiri Kosina wrote:

On Mon, 26 Feb 2007, Richard Purdie wrote:

quoted

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?

This should come from two calls to fbcon_generic_blank() in
drivers/video/console/fbcon.c with a different blank parameter and is
therefore in a way outside the scope of the backlight class.

It would be interesting to know why it decides to blank then immediately
unblank the display though. I've cc'd the fbdev-devel list.

Richard



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