[vfio-users] Crossfire - has anyone tried it?

[Taiidan at gmx.com]

On 02/12/2017 05:15 AM, Friedrich Oslage wrote:

> Crossfire requires a mainboard chipset which supports crossfire. Qemu
> can emulate a 440fx or q35 chipset, neither of them are listed in AMD's
> compatibility chart [1].
>
> AMD stopped using bridging ports a few years ago and switched to XDMA
> for GPU intercommunication. That means all communication is done via the
> PCI Express port, which requires quite a bit of support in the mainboard
> chipset. If would probably be easier to get an older Crossfire version,
> one which still uses interconnect bridges, or NVIDIA SLI, to work but
> both of them still require some level of support within the mainboard
> chipset.
>
> Regards,
> Friedrich
>
> [1] http://support.amd.com/en-us/kb-articles/Pages/Crossfire-Chart.aspx
>
> On 02/11/2017 05:33 PM, Taiidan at gmx.com wrote:
>> Has anyone tried this? does it work? I heard that you need to modify
>> the BIOS (Thus seabios) to provide license keys or something like that
>> or the drivers will refuse to enable it.
>>
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Card to card DMA communication that doesn't involve the host processor 
isn't anything special, as long as the root ports and bridge devices 
have PCI-e ACS there shouldn't be any issue (which rules out almost 
every intel board/cpu as they lack ACS, but I have an AMD opteron so I 
am ok)

Literally the only difference between a SLI/Xfire board and one that 
isn't is the license flag on the bios tables.

There was this guy who got it working XDMA but that was years ago.

https://www.redhat.com/archives/vfio-users/2015-September/msg00028.html