linux-kernel - Re: samsung-laptop backlight control not working

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Message-ID: <BANLkTi=bWpbRkt1tie44+MoXWfPdG_zZ+w@mail.gmail.com>
Date:	Wed, 1 Jun 2011 16:50:17 +0200
From:	David Herrmann <dh.herrmann@...glemail.com>
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org, mjg@...hat.com
Subject: Re: samsung-laptop backlight control not working

Hi Greg

On Thu, May 19, 2011 at 8:53 PM, David Herrmann
<dh.herrmann@...glemail.com> wrote:
> On Thu, May 19, 2011 at 8:27 PM, Greg KH <gregkh@...e.de> wrote:
>> On Thu, May 19, 2011 at 08:18:16PM +0200, David Herrmann wrote:
>>> Hi
>>>
>>> I tried the new samsung-laptop driver with samsung backlight support.
>>
>> What kernel are you trying?  We have some recent patches to the driver
>> to try to resolve some of these issues on your laptop.
>
> I use linus' tree. 2.6.39
>
>>> It is detected as:
>>> [109282.931433] samsung_laptop: found laptop model 'N150P/N210P/N220P'
>>>
>>> However, backlight support is kind of weird:
>>> "echo 1 >/sys/class/backlight/samsung/brightness"
>>> does not set brightness to 1 but instead reduces brightness for 1.
>>> That is, if my current brightness setting is 8, I need to call "echo 1
>>> >..." 7 times to get brightness value 1.
>>>
>>> "cat /sys/class/backlight...."
>>> returns 1 after the first try, though.
>>>
>>> "echo 3 >..."
>>> reduces brightness also for 1 but stops at brightness level 3 if I
>>> repeat the command.
>>>
>>> dmesg shows the following for every "echo" I call:
>>> [110690.073783] ACPI: Failed to switch the brightness
>>>
>>> Furthermore "echo 0 >..." doesn't disable backlight but instead
>>> behaves like a brightness setting below 1.
>>
>> Yeah, don't echo 0 there, that doesn't work to well.  I have some
>> patches here that you can try if you want, just let me know.
>
> That would be great! I have really no idea about acpi so I can't fix
> it myself. If you could give me some git tree where I can find them, I
> could test them.
>
>>> However, I know the following works on my machine:
>>> setpci -s 00:02.0 F4.B=255
>>> It accepts a setting between 0-255 and 255 is full brightness and 0 is
>>> backlight off.
>>
>> Don't do that, the video driver will not like you as you are changing
>> things without telling the bios that something is really happening.
>>
>> Of course you can continue to do this, it's just strongly not
>> recommended.
>
> Ouh, I didn't know that. It was recommended in some distro wiki so I
> tried it and it worked. Anyway, I thought it might give you some
> information about the N210 model.
>
>> thanks,
>>
>> greg k-h
>
> Thanks
> David

Maybe you missed that mail, any update on this? Where could I get
those patches? ;)

Thanks
David
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