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

[Daniel Drake]

Hi,

We are unable to boot Acer Aspire E5-553G (AMD FX-9800P RADEON R7) nor
Acer Aspire E5-523 with standard configurations because during boot
the screen is flooded with the following error message over and over:

  AMD-Vi: Completion-Wait loop timed out

We have left the system for quite a while but the message spam does
not stop and the system doesn't complete the boot sequence.

We have reproduced on Linux 4.8 and Linux 4.10.

To avoid this, we can boot with iommu=soft or just disable the amdgpu
display driver.

Looks like this may also affect HP 15-ba012no :
https://bugzilla.redhat.com/show_bug.cgi?id=1409201

Earlier during boot the iommu is detected as:

[    1.274518] AMD-Vi: Found IOMMU at 0000:00:00.2 cap 0x40
[    1.274519] AMD-Vi: Extended features (0x37ef22294ada):
[    1.274519]  PPR NX GT IA GA PC GA_vAPIC
[    1.274523] AMD-Vi: Interrupt remapping enabled
[    1.274523] AMD-Vi: virtual APIC enabled
[    1.275144] AMD-Vi: Lazy IO/TLB flushing enabled
[    1.276498] perf: AMD NB counters detected
[    1.278096] LVT offset 0 assigned for vector 0x400
[    1.278963] perf: AMD IBS detected (0x000007ff)
[    1.278977] perf: amd_iommu: Detected. (0 banks, 0 counters/bank)

Any suggestions for how we can fix this, or get more useful debug info?

Thanks
Daniel