https://bugs.freedesktop.org/show_bug.cgi?id=108521
--- Comment #27 from Robert Strube rstrube@gmail.com --- Thanks for the response.
I think it was just a coincidence that the eGPU started working with acpi=off. Taking a closer look at the issue it really does appear to be a BIOS problem that prevents the proper PCI resource allocation to one of the TB PCI bridges. In fact when I took a closer look at the dmesg with acpi=off I still see the resource issues present.
I've opened up an official bug report here with the kernel ACPI BIOS team here: https://bugzilla.kernel.org/show_bug.cgi?id=201527
I realize the issue should really be solved by the manufacturer, but perhaps the kernel devs can create a work around and/or have more direct lines of communication with the Dell engineers. Thank you both for your suggestions and comments.
Rob