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

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Date:	Mon, 13 Jun 2011 16:50:00 -0700
From:	Greg KH <gregkh@...e.de>
To:	David Herrmann <dh.herrmann@...glemail.com>
Cc:	linux-kernel@...r.kernel.org, mjg@...hat.com
Subject: Re: samsung-laptop backlight control not working

On Wed, Jun 01, 2011 at 04:50:17PM +0200, David Herrmann wrote:
> 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? ;)

Ick, sorry, they can be found at:
	http://git.kernel.org/?p=linux/kernel/git/gregkh/patches.git;a=tree

I need to push them to Michael soon, I've been swamped with other stuff
at the moment, sorry about this.

greg k-h
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