[Intel-gfx] Intel DRM Driver - Weathered Colours Patch

[nixuser1980]

Hello All,

Please find a proposed workaround patch for a weathered colours 
(incorrect assignment to Limited RGB setting) issue.
The weathered colour issue is documented at:

https://bugs.archlinux.org/task/46472
https://wiki.archlinux.org/index.php/Intel_graphics#Weathered_colors_.28color_range_problem.29
https://losca.blogspot.com.au/2013/11/workaround-for-setting-full-rgb-when.html


This patch, which I have shared with Jesse Barnes, provides a kernel 
command line option "i915.rgb_mode" with two usable options:

i915.rgb_mode=1 gives forced Full RGB Mode;
i915.rgb_mode=2 gives forced Limited RGB Mode.

Any other value passed to i915.rgb_mode will call the default Automatic 
RGB mode.

A limitation of this patch is that the KMS framebuffer needs to be 
interrupted, such as occurs when xorg-server starts.
i.e. if xorg-server were not to be started, the weathered colour issue 
remains in effect, even with a switch from one tty to another.
For reference, the machine that I am testing on is a 4770k (Haswell, 
Core i7).
I am investigating the issue further to improve this workaround so that 
the change from KMS to xorg-server is not required for the patch to come 
into effect.

I have tested this patch on Debian Testing.


-Damien Sticklen
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