[Bug 107476] DisplayPort and LSPCON always defaults to incorrect limited-range RGB on Intel Graphics for 24bpp+ displays

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107476

--- Comment #16 from Nicholas Stommel <nicholas.stommel at gmail.com> ---
The only displays I have available to test natively output 1920x1080 at 60Hz which
I suppose matches the entry in the table /* 0x52 - 1920x1080 at 60Hz */. I should
point out that hundreds, if not thousands of computer monitors (not televisions
or av equipment) output 1920x1080 at 60Hz. The odd thing here is that on each
1920x1080 at 60Hz monitor, over HDMI, full-range RGB 0-255 is always correctly
used, but over DisplayPort, limited-range RGB 16-235 is always incorrectly
used. 

That doesn't make sense, especially for displays with greater color bit depth
like commonplace 24bpp displays. These displays don't expect anything other
than full range color, and look awful without it. Intel's Windows drivers for
iGPUs correctly default to full range RGB on these displays over DisplayPort.
AMD and NVIDIA graphics cards drivers also correctly default to full range RGB
output for computer monitors on Windows and Linux. The discrepancy between
Intel's i915 driver module selecting different color ranges over HDMI and
DP/LSPCON is the problem here. 

The vast majority of monitors on the market also fit the modes in the table you
mentioned, even those with 4k HDR, so the logic behind the same 24bpp+ displays
*not* automatically receiving full-range color appropriately from Intel's Linux
driver over DP and LSPCON doesn't make sense, especially when they do correctly
receive full-range color over HDMI. I don't think this issue is about CEA/VESA
specifications. Rather, it concerns the subpar reality of incorrect,
limited-range, washed-out color on non-av equipment (computer monitors, namely)
over DP and LSPCON.

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