Re: [PATCH] Revert 95f408bb Ryzen DMA related RiSC engine stall fixes

[Mauro Carvalho Chehab <mchehab@kernel.org>]

Em Thu, 06 Dec 2018 18:18:23 +0100
Markus Dobel <markus.dobel@gmx.de> escreveu:

> Hi everyone,
> 
> I will try if the hack mentioned fixes the issue for me on the weekend (but I assume, as if effectively removes the function).

It should, but it keeps a few changes. Just want to be sure that what
would be left won't cause issues. If this works, the logic that would
solve Ryzen DMA fixes will be contained into a single point, making
easier to maintain it.

> 
> Just in case this is of interest, I neither have Ryzen nor Intel, but an HP Microserver G7 with an AMD Turion II Neo  N54L, so the machine is more on the slow side. 

Good to know. It would probably worth to check if this Ryzen
bug occors with all versions of it or with just a subset.
I mean: maybe it is only at the first gen or Ryzen and doesn't
affect Ryzen 2 (or vice versa).

The PCI quirks logic will likely need to detect the PCI ID of
the memory controllers found at the buggy CPUs, in order to enable
the quirk only for the affected ones.

It could be worth talking with AMD people in order to be sure about
the differences at the DMA engine side.

Thanks,
Mauro