[Intel-gfx] regression: 3.16, i915: less colors in X?, caused by 773875bfb6737982903c42d1ee88cf60af80089c

[Pavel Machek]

Hi!

> > > I just test-booted 3.16-rc1, and background in X looked just wrong --
> > > very noticeable bands on the background gradient. I thought that maybe
> > > it is just my eyes, but I went back to older kernel, and background is
> > > ok now.
> > > 
> > > I'm trying to figure out how to ask X what color depth it is using...?
> > > 
> > > This is thinkpad x60 with Debian 6.0.9.
> > > 
> > > Any ideas?
> > 
> > That suggests that the panel dithering changed. Compare intel_reg_dumper
> > output for both kernels, especially PIPE.CONF.

intel_reg_dumper has so many dependencies that it is basically
impossible to get working :-(.

Anyway, this seems to be the problem; if I revert it, my colors are
back.

commit 773875bfb6737982903c42d1ee88cf60af80089c
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Mon Jan 27 10:00:30 2014 +0100

    drm/i915: Don't set the 8to6 dither flag when not scaling
    
    Apparently we really only need this when the pfit is enabled, at
    least
    I couldn't dicern any difference here. Furthermore the hacks we
    have
    to reconstruct this bit is a bit glaring, and probably only works
    because we can't move the lvds port to any other pipe than pipe B
    on
    gen2/3.
    
    So let's just rip this out.
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77137 (the
    LVDS
    WARNING log, not the main "VGA can't be turned on" issue).
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html