The problems with ARC GPU passthrough also bothered me for quite a while (same "not ready XXms after FLR: waiting" issue).
My issues:
It is fine to simultaneously passthrough the entire card (video and audio) to a VM, no matter whether ReBAR is enabled or not.
But on shutdown of the VM, "not ready XXms after FLR: waiting" is reported in syslog. After waiting for some time, "device inaccessible" is reported and I lost the card. I must hard reboot the machine to get it back.
My server setup:
MSI MAG B550M MORTAR MAX WIFI
Intel ARC A380 index from GUNNIR
AMD 5600G CPU
Unraid Version: 6.12.4
ReBAR is enabled in BIOS. It can also be confirmed in a Win10 VM with the official Intel Arc Control software.
It is solved by the following scripts (so I run them with the User Scripts plugin and set it to run "At Startup of Array"):
#!/bin/bash
echo > /sys/bus/pci/devices/0000:12:00.0/reset_method
echo > /sys/bus/pci/devices/0000:13:00.0/reset_method
Note that these scripts must be executed before the shutdown of VMs. Modify the physical address to your own case.
I just need to run these scripts one time on each startup of the server, and I can flawlessly shutdown the VMs with perfect performance of the Intel ARC A380 GPU. No error lines are reported on logs.
Not sure if this is what you need. It seems that with Linux Kernel 6.2+, compatibility issues are resolved, but I would just wait for Unraid offical releases because stability is much more important to me.