dual RX460 result in logspam about P2P DMA

[Alex Deucher]

On Sat, May 15, 2021 at 10:12 AM Richard Dietrich Wachler
<rwachler at posteo.net> wrote:
>
> Excuse my novicesness,
>
> i use 2 RX460 on a KGPE-D16 server board to drive 4 displays.
>
> 02:00.0 VGA compatible controller: Advanced Micro Devices, Inc.
> [AMD/ATI] Baffin [Radeon RX 460/560D / Pro
> 450/455/460/555/555X/560/560X] (rev cf)
> 06:00.0 VGA compatible controller: Advanced Micro Devices, Inc.
> [AMD/ATI] Baffin [Radeon RX 460/560D / Pro
> 450/455/460/555/555X/560/560X] (rev cf)
>
> There is a noticeable mouse lag on the second card, so i investigated
> and got logspam 20 times a second like this:
>
> May 15 15:58:27 xx kernel: amdgpu 0000:02:00.0: cannot be used for
> peer-to-peer DMA as the client and provider (0000:06:00.0) do not share
> an upstream bridge or whitelisted host bridge
>
> It seems there is no real way to disable the check or disable P2P DMA
> completely. Or maybe my problem is elsewhere?
>
> Thanks for any hints, i havent found anything about this as its quite a
> new feature.

Fixed in this patch:
https://patchwork.kernel.org/project/dri-devel/patch/20210517115705.2141-1-christian.koenig@amd.com/

Alex