I hope this is the correct place to ask this(?). I'm not sure if my 
large attachments will come through; this is my first attempt.

I'm having problems getting this 4-port 2.5Gbps NIC to be stable. I have 
tried on multiple different physical systems both with Xeon server and 
i7 workstation chipsets and it behaves the same way on everything. 
Testing with latest Arch Linux and kernels 6.1, 6.2, and 5.15. I'm using 
the kernel default r8169 driver.

The higher the load on the NIC the more likely the whole system freezes 
hard. Everything freezes including my serial console, SysRq doesn't 
work, even the motherboard hardware reset switch doesn't work(!). I have 
to cut power to the system to reset it.

Disabling IOMMU is more stable but doesn't fix the issue. ASPM doesn't 
work correctly on this card either despite the ASMedia 1812 supposedly 
supporting it (lots of corrected PCIe errors). Enabling or disabling 
ASPM makes no difference.

"SSU-TECH" (generic/counterfeit?) 4-port 2.5Gbps PCIe x4 card
   ASMedia ASM1812 PCIe switch (driver: pcieport)
   RTL8125BG x4 (driver: r8169)

I have tested with a normal network configuration consisting of multiple 
machines and also with lookback cables plugging the card ports in to 
itself.

I have attached the scripts I use with the loopback cables 
(crashsys.sh), lspci, and dmesg.

System freezes almost immediately with:
   3,1266,4284361895,-;pcieport 0000:04:02.0: Unable to change power 
state from D3hot to D0, device inaccessible
    SUBSYSTEM=pci
    DEVICE=+pci:0000:04:02.0

If I set permanent D0 mode (power/control=on) then the error is 
different when the system freezes:
   r8169 0000:0d:00.0 enp13s0: rtl_chipcmd_cond == 1 (loop: 100, delay: 
100).

Is there anything I can do to get more debugging information? The system 
locks so hard that I haven't gotten much so far. It's unclear if the 
problem is happening in the pcieport driver, r8169, or somewhere else.