Howto Lower brightness on Apple LCD Monitor? KUbuntu 10.4, KDE System Settings Display; jor XOrg

Éric Piel E.A.B.Piel at
Thu Jun 24 02:41:25 PDT 2010

Op 23-06-10 17:38, Alex Deucher schreef:
> On Wed, Jun 23, 2010 at 11:11 AM, Xavier Bestel <xavier.bestel at> wrote:
>> On Wed, 2010-06-23 at 00:41 +0200, Éric Piel wrote:
>>> Op 22-06-10 23:56, giovanni_re schreef:
>>>> Didn't get an answer on KUbuntu list, so hopefully someone here might
>>>> have a suggestion.
>>>> ==
>>>> I've just installed an Apple Cinema Display (LCD) monitor. This is a 5
>>>> year old monitor.
>>>> Using KUbuntu 10.4
>>>> The apple website indicates this monitor has:
>>>> User controls (hardware and software):
>>>>     Display power, system sleep, system wake, brightness and display tilt
>>>> Brightness is what I want to turn down.
>>>> Looking in the
>>>> KDE System Settings > General > Computer Administration > Display > Size
>>>> & orientation > DVI-0
>>>> there is no adjustment for brightness.
>>>> Anyone know how to decrease brightness on this?
>>>> What sw manages the KDE system settings for Displays?  KDE? X?
>>>> Is there a way to turn down the brightness using some X config?
>>>> Is there a GUI for doing X configuration settings?
>>> Why do you think you can change the brightness via software? It is very
>>> unsual for separate monitors to support this. Isn't there some buttons
>>> on the monitor to do that?!
>>> Anyway, if you really want to do this by software:
>>>  * DDC/CI is the key. Try using ddccontrol. But your graphic card must
>>> support it, and your monitor too. In practice, it's unlikely to work.
>> Well, it works quite well on my Dell 24" (radeon driver), even if it has
>> front controls.
>> I think more monitors support this than you think. The problems are:
>> - KMS/Xorg don't support it, so you have to be root for ddccontrol to
>> work.
> KMS exposes the ddc i2c buses via sysfs, so you can access them
> directly.  It would be pretty easy to add some common ddc/ci code to
> the drm and then expose whatever controls are found via sysfs and
> xrandr as connector attributes similar to the edid.  I'd be happy to
> help if someone more familiar with ddc/ci wanted to get the ball
> rolling.
Could be useful. Becareful though, apparently, there was already a DDC
driver in the kernel and it was kicked out because everything can be
done in userspace:

By the way, on my i945, I modprobe'd i2c-dev, the 2 i2c's of the graphic
card seems being fine in sysfs, but when I run "ddccontrol /dev/i2c-0",
it behaves exactly as if the file didn't exist, because apparently it
tries to do some weird things with ddcpci :-S


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