Overlay plane: position not updated when CRTC_X is negative

Brief summary of the problem:

I'm using an overlay plane to display a 24x24 buffer. I'm moving it around by changing its position (CRTC_X and CRTC_Y).

Sometimes I set a negative position for the plane. For instance:

    │       ├───"CRTC_X" (atomic): srange [INT32_MIN, INT32_MAX] = 227
    │       ├───"CRTC_Y" (atomic): srange [INT32_MIN, INT32_MAX] = -4

This seems to work fine as long as CRTC_Y is negative. However, when I set CRTC_X to a negative value like so:

    │       ├───"CRTC_X" (atomic): srange [INT32_MIN, INT32_MAX] = -4
    │       ├───"CRTC_Y" (atomic): srange [INT32_MIN, INT32_MAX] = 123

The update is ignored by amdgpu, and the overlay is stuck in the previous positive position.

In other words, after setting CRTC_X to a negative value, all CRTC_Y changes are ignored.

Hardware description:

• CPU: AMD Ryzen 5 3500U
• GPU: APU (PCI 1002:15d8 Advanced Micro Devices, Inc. [AMD/ATI] Picasso)
• System Memory: 6GiB
• Display(s): integrated screen
• Type of Diplay Connection: eDP

System infomration:

• Distro name and Version: Arch Linux
• Kernel version: ~agd5f/linux, drm-next branch, commit 7ff818f97c30
• Custom kernel: N/A
• AMD package version: N/A

How to reproduce the issue:

1. Clone gamescope
2. Apply this patch to stop setting ALLOW_MODESET on all commits: https://l.sr.ht/DHTC.txt
3. Build gamescope
4. Run it with Steam and enable use of KMS planes: build/gamescope -e -l -d -- steam -tenfoot -steamos >gamescope.log 2>&1
5. Start Portal 1
6. Move the cursor to the left edge of the screen, then move it vertically