ZisWorks Dual DP monitor not configuring properly with TILE

Brief summary of the problem:

ZisWorks monitors are off-the-shelf consumer displays, modified with custom tcon/dp/psu, to be able to drive the display at various modes. 1920x1080@240hz and 3840x2160@120hz being the most used. The latter uses EDID tile information to join two halves of the monitor into one, using a dp cable for each half.

Hardware description:

• CPU: AMD Ryzen 1700
• GPU: Asrock Radeon RX 5700 XT
• System Memory: 64gb ddr4
• Display(s): Dual ZisWorks X28 Rev2 Kit for Samsung U28H750
• Type of Display Connection: Dual DP

System infomration:

• Distro name and Version: Gentoo ~amd64 and Arch Linux
• Kernel version: 5.8
• AMD package version: not sure what to put here. nothing outside standard libdrm/mesa.

How to reproduce the issue:

1. get an amdgpu with enough dp ports to run one.
2. boot into linux, start xorg up. (mate and i3wm tested)
3. enable the 4k120hz mode of the monitor
4. attempt to configure the monitor using xrandr
5. no output on monitor Earlier kernel versions did show output on the 4k mode, however, there was lack of sync/skew between both halves. agd5f_ had previously had a patch here which fixed the issue, but the patch is no longer applicable to current kernel versions.

Attached files:

• Dmesg log: dmesg.log
• Xorg log: Xorg.0.log