changing LVDS contrast level on Thinkpad with M22 [Mobility Radeon X300] -- is it possible?

Alex Deucher alexdeucher at
Mon Jan 12 07:40:53 PST 2009

On Sun, Jan 11, 2009 at 2:08 PM, Bradley M. Kuhn <bkuhn at> wrote:
> I am using an IBM Thinkpad T43 2668-6ZU.  My goal is to change the
> contrast setting on the LVDS panel, which is not possible with any of
> the IBM hotkeys, etc.  I have checked the default proprietary ATI
> utilities that come with the Microsoft Windows XP drivers, and they have
> a setting for LVDS contrast between "0" and "200".  I note that the
> proprietary ATI fglrx driver *is not* able to change this contrast
> setting.
> I want to be clear here that I am not talking about the XVideo contrast
> changing which can be done with xvattr -- that works with applications
> that use the XVideo extensions, but only changes the video itself.
> The LVDS itself has a native contrast setting that I only discovered
> myself recently when switching to a laptop that had a native setting
> that was extremely high contrast and difficult to use.  Of course, with
> a standard monitor, you can just adjust it with standard settings, but
> IBM Thinkpads have only brightness and no contrast settings.
> I have tried both ddccontrol and radeontool to attempt to change this.
> Below are the results from ddccontrol attempts, and the output of
> registers given by radeontool.  I simply don't know enough to figure out
> what register I should try to change for this setting, and I would
> appreciate any suggestions that anyone has.  I read the source of both
> ddccontrol, the radeonfb Linux driver, and the radeon xorg driver, but I
> simply don't know enough about low level video card programming to be
> useful in this regard, but would be happy to help figure it out by
> trying things on this hardware.
> Thanks!

I don't know of any contrast interface in on the GPU.  Are you sure
xgamma (or xrandr --gamma on newer xservers and xrandr versions) which
adjusts the crtc CLUT won't do what you want?  I suspect if there
really is a contrast control on some laptops,  it's probably
implemented via some LCD specific interface controlled either by gpio
from the gpu or by some controller hung off the motherboard.
Generally, unless you know what you are doing it's not a good ideal to
play with the gpio lines on the GPU.


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