[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 #9 from Nicholas Stommel <nicholas.stommel at gmail.com> ---
Created attachment 141021
  --> https://bugs.freedesktop.org/attachment.cgi?id=141021&action=edit
dmesg-lspcon

This limited default RGB problem extends to DP-LSPCON HDMI connections, which
is the scenario many of those affected are also posting about. My computer
happens to have a full-size 'native-looking' HDMI port option board attached to
the motherboard through LSPCON. This helpful information from Intel i915 dev
Imre Deak cleared up my confusion about why a hardware HDMI port is recognized
as a DisplayPort (DP-3 in my case): "There are two ways to connect HDMI to the
APL RVPs: via the DDI1 DP++ plug with an DP->HDMI dongle, or via the DDI0 HDMI
plug which is connected to the SoC through the LSPCON converter. You seem to be
using the second scenario with LSPCON being in the protocol converter mode
(configured as such by BIOS). In that case the connection will show up as a DP
connector." Anyway, it appears that the incorrect color mode selection extends
to DP-LSPCON.

The following information is for the DP-LSPCON to HDMI connection which, like
regular DisplayPort, incorrectly defaults to limited range RGB 16-235 on the
same monitor (Samsung CF591) and same machine. The latest drm-tip kernel with
the parameters "drm.debug=0x1e log_buf_len=10M" was used. Attached file
"dmesg-lspcon-hdmi.txt" contains the full output of dmesg using HDMI truncated
at one minute after boot (the file is large and most of the useful i915 debug
info is much closer to the beginning of the file). "xrandr --verbose" output is
also attached as "xrandr-lspcon-hdmi.txt".  

-- Occurrence: Color range detection is never correct over DP-LSPCON to HDMI,
always defaults to limited-range RGB
-- Chipset: Intel® Core™ i7-7700T CPU using Intel® HD Graphics 630 (Kaby Lake
GT2)
-- System architecture: x86_64
-- Kernel version (drm-tip) 4.18.0-994-generic
-- Linux distribution: Ubuntu 18.04.1 LTS (also confirmed on Fedora 28, appears
distro-independent)
-- Machine: HP Elitedesk 800 G3 DM 35W
-- Display connector: DP-LSPCON to HDMI

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