[i915] Backlight brighter since 3.9.0

[Jan Hinnerk Stosch]

2013/5/20 Daniel Vetter <daniel at ffwll.ch>

> 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.
>
> Cheers, Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>

Ok, thank you for your detailed explanation.

Regards,
jhs
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