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Old 01-19-2009, 11:28 AM   #1
gbloon
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Laptop screen brightness; constantly reverts to minimum


Running Slackware 12.2 on Acer 5710 Laptop.

During boot the screen is bright enough until ACPI is loaded, and then immediately goes to minimum brightness.
Once booted I can use the hardware keys to increase the brightness.
But when I start X; the screen is dimmed all the way down again.
Anytime DPMS blanks the screen when idle, the screen comes back minimum brightness again. Same thing with suspend. I can raise the brightness with the keys (hold down Fn and hit right-arrow many times), but I hate having to do this again and again and again.... it's a real pain.

I would like to know why it is doing this, and how it might be possible to stop it!
 
Old 01-20-2009, 08:37 AM   #2
skuzye
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Hello, my system turns brightness setting to the minimum when I unplug AC Adapter, notice that you can turn it back and it shouldn't change anymore (maybe if you plug and unplug AC Adapter again .

Sure it can be a software issue but it doesn't hurt to check if something is wrong with your ac adapter or your cable (experience showed that sometimes such weird things happens to us and drives us crazy looking for something that is right in front of you).

You could unplug it, set brightness up and test if it turns down again in the desirable situations.

BTW, is acer modules for acpi loaded ?


Edit: You are at the wrong forum. You should have posted to Linux - Laptop.

Skuzye

Last edited by skuzye; 01-21-2009 at 06:37 AM.
 
Old 01-20-2009, 01:14 PM   #3
gbloon
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Hi Skuzye, and thanks for replying.

Plugging and unplugging the AC adapter has absolutely no effect on screen brightness on my system. It does not change at all.

As for Acer modules, the only one I see loaded is acer_wmi. I must confess I have no idea what this is for. Can you tell me? Is there anything else I should have loaded?

Gbloon
 
Old 01-21-2009, 06:42 AM   #4
skuzye
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Ok, I have to be honest with you, I don't really know what's happening but if you have no better idea we can check a few things and maybe we or someone can help you figure out what's wrong.

You have the right module loaded (that's obvious since you can change brightness with your keyboard).


You should try to disable DPMS: if DPMS is the issue (probably not it but a wrong setting or a missing one) when you startx DPMS is activated so it turns down the bright and when it comes in action again (blank screen) and does it again.

If turning it off solves the problem then try to find some documentation about it, if not, let us know and let's think again.

Skuzye
 
Old 01-22-2009, 05:13 AM   #5
gbloon
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I disabled DPMS, then set the KDE power control to turn off the screen. Just as before, the display resumes at minimum brightness. Every time the display is restarted, it is at minimum brightness, regardless of HOW it is turned off (by DPMS, suspend/hibernate system, restart X server) -- EXCEPT that closing the lid (which blanks the screen with ACPI) does not change the brightness when it the screen comes back on when the lid is raised.

Now, here is something strange. /proc/acpi/video/VGA/LCD/brightness lists 10 levels, from 10 to 100 by 10's - and the current level. With a fully bright screen, I see the current level is 100. Now I dim the screen with the hardware keys - and look at the current level; it is STILL 100. But, if I now echo the value 100 and redirect into the brightness file, the screen becomes fully bright!
I shut down X, and check "current level"; it is 100. Start X again - screen is fully dim, but current level still shows 100. So the screen brightness level can be controlled by making an ACPI setting, but that setting - which is persistent - does not cause the brightness to restore correctly except after an ACPI event, such as lid closure. Normal screen blanking by idle timeout is not an ACPI event so the level is not restored. But, why does it change at all? It has been set by hardware keys; surely it should remain in that state until something changes it. X does not mess with monitor brightness. So what is making it always start fully dim?
 
Old 01-22-2009, 07:31 AM   #6
skuzye
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Have you tried suspending while not running X? You can do it using ACPI.

This way we can see if it's X related or not.

Although, I'm suppose that ACPI has nothing to do with brightness because my laptop doesn't have support for video module ACPI and I can change brightness normally.

Try to unload this module, maybe there are more than one process fighting for it.

Skuzye
 
Old 01-22-2009, 11:56 AM   #7
gbloon
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Well, you did not say which module to unload, but anyway I looked at the output of lsmod and thought "video" might be a good place to start. So I killed X, removed the module "video", started X again and -- bingo! No more dimming. It stays at the level I set, through DPMS blanking and a system suspend. And if I stop X and start it up again, the brightness is still as previously set. The lid close screen blanking event also still works. I have not so far found any adverse consequences of running without the module - so I have blacklisted it.

Thanks for getting involved, Skuyze!
 
Old 01-23-2009, 07:25 AM   #8
skuzye
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I seems that as I said before something was fighting to control brightness and it was video module from ACPI.

I'm sorry I didn't say what module to unload but very happy that you could figure it out for yourself.

It's fun to solve problems like this when you really don't know what's happening. Thank you for the fun (:

Skuzye
 
  


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