I've found the exact commit!

https://lists.freedesktop.org/archives/amd-gfx/2018-July/023920.html

Fixes the issue against a few kernels affected but my issue is that the code
base has been modified so heavily while retaining the same behavior that I
can't apply this to kernel 5.2 linux-stable git.

I can't even discern where to manually edit the related files to change the
behavior.

It may be necessary to include another fix that that list of related patches to
fix the behavior for my connector/ panel. Not a programmer myself so I'm not
sure what's supposed to happen here.