[vfio-users] How does bios rom file work?
Nick S
nick.kvmhv at gmail.com
Sat Jan 6 23:27:00 UTC 2018
I realized that I don't quite understand how does the ROM file that we can
pass in QEMU command line work. I have three cards of the same model but
coming from the different vendors. When I extract ROMs from these cards, I
get different files. The card on the boot slot gives a much smaller file
and other two cards give files of slightly different sizes:
-rw-rw-r-- 1 nick nick 118784 Dec 14 21:53 vbiosrx480_03.rom
-rw-rw-r-- 1 nick nick 58880 Dec 14 21:53 vbiosrx480_04.rom
-rw-rw-r-- 1 nick nick 118272 Dec 14 19:57 vbiosrx480_06.rom
I am also seeing the following error in dmesg:
[Sat Jan 6 09:26:58 2018] vfio-pci 0000:04:00.0: Invalid PCI ROM header
signature: expecting 0xaa55, got 0xffff
[Sat Jan 6 09:26:58 2018] vfio-pci 0000:04:00.0: Invalid PCI ROM header
signature: expecting 0xaa55, got 0xffff
But other than that the card actually works without issues. So, the
questions I have are:
1) What is the significance of this ROM file and why is it needed?
2) What would happen if I apply some changes to it? For example, I can edit
it in Polaris bios editor. If I change the memory timings and use that
changed file, will it take effect when this GPU is assigned to a VM or
would the actual flashed bios take precedence?
3) What should I expect if I use bios from one maker of, say, Radeon 480 RX
on the same model another maker (i.e. Sapphire vs AMD)?
Thank you,
Nick
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