[Bug 110496] [GLK] no signal - with samsung 4k TV - HDMI UHD Color (ENABLED)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110496

--- Comment #35 from teeedubb at gmail.com ---
Created attachment 145907
  --> https://bugs.freedesktop.org/attachment.cgi?id=145907&action=edit
Chroma subsampling test in 4k60 non UHD Color mode

I haven't been able to find a method in software to check what level of chroma
subsampling is being used with the 4k60 modeline in non UHD color mode, but I
found a visual test that indicated that 4:4:4 is being used - I could read all
the lines clearly from about6m away on a 65' TV. Closeup photo attached of the
bottom two lines.

So it seems that the GLK GPU doesnt agree with the UHD color mode EDID, but the
modes that are exclusive to it can be forced via a custom modeline when not in
UHD color mode.

https://www.geeks3d.com/20141203/how-to-quickly-check-the-chroma-subsampling-used-with-your-4k-uhd-tv/

I didn't have any luck using modelines I found for a similar issue on
askubuntu, so these may not work for other TVs, but here the three additional
ones that are present in UHD color mode.

xrandr --newmode "3840x2160_60.00" 594.000 3840 4016 4104 4400 2160 2168 2178
2250 +hsync +vsync
xrandr --newmode "3840x2160_59.94" 593.407 3840 4016 4104 4400 2160 2168 2178
2250 +hsync +vsync
xrandr --newmode "3840x2160_50.00" 594.000 3840 4896 4984 5280 2160 2168 2178
2250 +hsync +vsync

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