Can't get RX 6700 XT running on Raspberry Pi CM4

Brief summary of the problem:

I'm trying to get an RX 6700 XT working on a Raspberry Pi Compute Module 4. When I compile amdgpu support into the 5.14.x Linux kernel and run sudo modprobe amdgpu, the Pi completely locks up—no response on mouse or keyboard, or via SSH or serial, or any other interface.

I have to hard-reboot the Pi to get back to a state where anything works.

Hardware description:

• CPU: ARM Cortex-A72
• GPU: Radeon RX 6700 XT
• System Memory: 4 GB
• Display(s): HP EliteDisplay E231
• Type of Diplay Connection: HDMI

System information:

• Distro name and Version: Raspberry Pi OS (based on Debian 10), latest
• Kernel version: 5.14.2 (built from current kernel source)
• Custom kernel: Kernel from Raspberry Pi OS fork, configs: Enable the Toneport UX1 Line 6 audio i/f / 5b7e7c238fef4f6f8d89ee8f65e7a37d8dc05176
• AMD package version: No package, compiled in kernel

How to reproduce the issue:

1. Power Raspberry Pi Compute Module 4 IO Board and Radeon card from external 700W power supply.
2. Compile kernel from rpi-5.14.y source tree with AMDGPU enabled via menuconfig
3. Blacklist the amdgpu driver at boot.
4. Boot the Pi.
5. Run sudo modprobe amdgpu.

Attached files:

Dmesg log: dmesg-pi-cm4.txt

More details also available (including more of my debug process) in this GitHub issue: Test GPU (AMD Radeon RX 6700 XT).