[Bug 111876] AMD 5700 XT / Navi - BenQ XL2420G - No EDID read with DP connector, HDMI works fine

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111876

            Bug ID: 111876
           Summary: AMD 5700 XT / Navi - BenQ XL2420G - No EDID read with
                    DP connector, HDMI works fine
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: not set
          Priority: not set
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: christopherjordan87 at gmail.com

Created attachment 145598
  --> https://bugs.freedesktop.org/attachment.cgi?id=145598&action=edit
dmesg output when using DP

I recently built a new machine (specs below), but I'm having trouble using the
display port connector with my old monitor (BenQ XL2420G) - I get the following
EDID error:

[drm:dc_link_detect [amdgpu]] *ERROR* No EDID read.

Following instructions to manually use an EDID appears to do nothing
(https://wiki.archlinux.org/index.php/kernel_mode_setting). I generated an EDID
with the "read-edid" package after modprobe-ing i2c-dev and HDMI connected, as
well as my old machine's nvidia card via "acquire EDID" in nvidia-settings.

I'm not sure how quirky other G-Sync or high-refresh-rate monitors are, but
this one *only* allows a 144 Hz refresh rate with display port. However, using
HDMI, everything appears to be fine. My Windows partition in the same machine
appears quite happy to use DP at 144 Hz, so I'm particularly baffled as to why
linux is struggling. After scouring the internet, it appears no one else has
the same issue, so it is possible that this monitor is simply not playing
nicely.

I have supplied my lspci output, as well as dmesg outputs with "drm.debug=0x1e
log_buf_len=4M" for both DP and HDMI connected. I am running up-to-date
archlinux, using linux-firmware from the testing repo (which should just be
neatly providing the navi firmware in a non-AUR package) and a bunch of
packages from the mesa-git repo. My pacman -Q is also attached.

Any help would be greatly appreciated! Many thanks in advance.

ASUS TUF Gaming X570-PLUS WiFi
AMD Ryzen 3900X
Powercolor Red Devil 5700 XT

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