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

[Alex Deucher <alexdeucher@gmail.com>]

On Thu, Dec 6, 2018 at 1:05 PM Mauro Carvalho Chehab <mchehab@kernel.org> wrote:
>
> 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 original commit also mentions some Xeons are affected too.  Seems
like this is potentially an issue on the device side rather than the
platform.

>
> 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.
>

It's not clear to me what the pci or platform quirk would do.  The
workaround seems to be in the driver, not on the platform.

Alex