[i915] Backlight brighter since 3.9.0

[Aaron Plattner]

On 05/20/2013 02:55 PM, Daniel Vetter wrote:
> On Sat, May 18, 2013 at 12:39:14AM +0200, Jan Hinnerk Stosch wrote:
>> Hallo,
>>
>> I hope this is the right place to ask, because I actually don't know
>> whether it is a bug or a feature that I'm experiencing since linux 3.9:
>> When I boot my system the backlight gets extremely bright compared to older
>> kernel versions. It is most obvious when I leave X (more a yellow than a
>> black background), but I have the impression, that the colors in X are
>> brighter than usual, too.
>> I used my spare time this afternoon to do a kernel bisect and learned that
>> the first "bad" commit is 55bc60db5988c8366751d3d04dd690698a53412c. As I
>> don't have insight or understanding of the code: Is this behaviour intended
>> and how could I change it to the old state or is it a bug and should I
>> report it somewhere?
>> My system is as follows:
>> Intel i5-3570k with Intel HD 4000
>> my monitor is connected via HDMI.
>> If you need any more information just tell me.
>
> Yeah, this is a feature. HDMI has (for oddball backwards compat with
> analog TV signals) a special mode which reduces the useable RGB value
> range by chopping off about 10% at the bottom and top end. This results in
> light colors getting brighter and dark colors getting darker.
>
> The above mentioned commit tries (to the best of our knowledge) to
> auto-set the option which most likely fits what the hdmi sink will do with
> the color data. You can either fix this up in the hdmi sink with the
> on-screen menu or by manually setting the "RBG Broadcast" property for the
> relevant hdmi connector to the setting you want.

This property seems like it's generally useful for all GPUs that support 
range compression.  Has anyone started the process of adding it to 
randrproto.txt as an official property?

http://cgit.freedesktop.org/xorg/proto/randrproto/tree/randrproto.txt#n1723

-- 
Aaron

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