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

[Alex Deucher]

On Wed, Jun 23, 2010 at 11:11 AM, Xavier Bestel <xavier.bestel at free.fr> 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
>> > http://support.apple.com/kb/SP79
>> > http://support.apple.com/kb/SP77
>> >
>> > 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.

Alex

> - Controls aren't standardized, so you have to play with the 255
> possible controls to find the useful ones (e.g. brightness and color
> temp).
>
>        Xav
>
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