Comment # 6 on bug 1190854 from Hadrien Grasland

Created attachment 853412 [details]
dmesg log with 32-bit mappings forced and resizable BAR disabled

I found two firmware settings related to device memory mappings:

1. One that inhibits mapping 64-bit integrated devices above 4 GB.
2. One that disables resizable BAR support.

Strangely enough, these two firmware settings seem to be interdependent:

- If I try to force 32-bit mappings without disabling resizable BAR, then
nothing changes in dmesg, and on my next trip to the UEFI setup screen I see
that the 32-bit mapping setting was silently reverted back off by the firmware.
- If I try to disable resizable BAR support without forcing 32-bit mappings,
then I still see messages about BAR resizing in dmesg, suggesting that the
change was ineffective. However, resizable BARs are still marked as disabled on
my next trip to the UEFI setup screen.
- If I force 32-bit mappings AND disable resizable BARs, then I get the
enclosed log. AMDGPU initialization still fails, and GPU VMEM detection is
still broken, but all the logs about BARs that were previously present are
gone, suggesting that at least this did something.