amd-iommu: can't boot with amdgpu, AMD-Vi: Completion-Wait loop timed out

['joro@8bytes.org']

On Tue, Mar 21, 2017 at 04:17:40PM +0000, Deucher, Alexander wrote:
> > -----Original Message-----
> > From: 'joro at 8bytes.org' [mailto:joro at 8bytes.org]
> > Sent: Tuesday, March 21, 2017 12:11 PM
> > To: Deucher, Alexander
> > Cc: Alex Deucher; Daniel Drake; Chris Chiu; amd-gfx at lists.freedesktop.org;
> > Nath, Arindam; iommu at lists.linux-foundation.org; Suthikulpanit, Suravee;
> > Linux Upstreaming Team
> > Subject: Re: amd-iommu: can't boot with amdgpu, AMD-Vi: Completion-Wait
> > loop timed out
> > 
> > On Tue, Mar 21, 2017 at 04:01:53PM +0000, Deucher, Alexander wrote:
> > > It seems to only affect Stoney systems, but not others (Carrizo,
> > > Bristol, etc.).  Maybe we could just disable it on Stoney until we
> > > root cause it.
> > 
> > Completion-wait loop timeouts indicate something is seriously wrong. How
> > can I detect whether I am running on a 'Stoney' system?
> 
> + John
> 
> I'm not sure if the iommu ids are different on stoney systems compared to Carrizo/Bristol systems.  The pci ids of the GPUs are different.  Stoney parts have 0x98E4 as the pci id for the GPU.
> 
> > 
> > Other question, a shot into the dark, does the GPU on these systems have
> > ATS? Probably yes, as they are likely HSA compatible.
> 
> Stoney is a small APU.  Kind of a mini Carrizo.  While it may claim to support ATS, I don't think it was ever validated on Stoney, only Carrizo/Bristol.

Okay, so maybe ATS is broken in some way on these chips. When queue
flushes happen it will also send the ATS-invalidates, and a queue flush
can cause a storm of those. This may be the issue.

I am preparing a debug-patch that disables ATS for these GPUs so someone
with such a chip can test it.


	Joerg