[XS] Change in coreboot[main]: mb/pcengines/apu2: don't enable IOMMU

[Felix Held (Code Review)]

Attention is currently required from: Felix Held, Krystian Hebel, Michał Żygowski, Piotr Król.

Hello Krystian Hebel, Michał Żygowski, Piotr Król, build bot (Jenkins),

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/79896?usp=email

to look at the new patch set (#2).

Change subject: mb/pcengines/apu2: don't enable IOMMU
......................................................................

mb/pcengines/apu2: don't enable IOMMU

Drop the enabling of the IOMMU device from all variant's devicetrees,
since there's something broken with either the IVRS table or possibly
the IOMMU itself. This fixes the issue of the Linux kernel stalling for
about 20 seconds right after printing 'AMD-Vi: Virtual APIC enabled' and
only getting unstuck when the periodic NMI results in a backtrace being
printed. This was tested with Debian running kernel 5.10.0-27-amd64, but
the same issue also showed up with newer kernels.

The official APU2 images don't show this bug, but there the IVRS isn't
generated by default.

TEST=Disabling the IOMMU which results in no IVRS being generated fixes
the bug.

Signed-off-by: Felix Held 
Change-Id: If74a7c64f53903fec0c01a55e1b202e800f02986
---
M src/mainboard/pcengines/apu2/variants/apu2/devicetree.cb
M src/mainboard/pcengines/apu2/variants/apu3/devicetree.cb
M src/mainboard/pcengines/apu2/variants/apu4/devicetree.cb
M src/mainboard/pcengines/apu2/variants/apu5/devicetree.cb
4 files changed, 0 insertions(+), 4 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/96/79896/2