Can't assign BARs / pcim_iomap_regions() failed loading gowin_pcie_demo

[kevpatt]

Problem shown in dmesg:

pci 0000:0f:00.0: BAR 0 [mem size 0x00100000 64bit]: can't assign; no space
...
gowin_pcie_demo 0000:0f:00.0: pcim_iomap_regions() failed. (-22)
...
probe with driver gowin_pcie_demo failed with error -22

Workaround:

1. Edit /etc/default/grub
   # nano /etc/default/grub
2. Make sure GRUB_CMDLINE_LINUX_DEFAULT includes iommu=pt and pci=realloc=on:
   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash iommu=pt pci=realloc=on"
3. Update grub:
   # update-grub
4. Reboot and try to load the gowin_demo.ko module again.