REGRESSION in 6.0-rc7 caused by patch "ARM/dma-mapping: use dma-direct unconditionally"

[Marek Behún]

Hello Linus, Arnd, Robin and Christoph,

I just bisected a regression on Turris Omnia (Armada 385), wherein the
system hangs shortly after init is run, to commit

  ae626eb97376 ("ARM/dma-mapping: use dma-direct unconditionally")
  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ae626eb97376

In order to fix the regression, I had to revert this commit and
subsequent 3 commits:
  ae626eb97376 ("ARM/dma-mapping: use dma-direct unconditionally")
  42998ef08aba ("ARM/dma-mapping: drop .dma_supported for IOMMU ops")
  d563bccfa35b ("ARM/dma-mapping: consolidate IOMMU ops callbacks")
  4136ce90f079 ("ARM/dma-mapping: merge IOMMU ops")
in reverse order, of course:
  git revert 4136ce90f079
  git revert d563bccfa35b
  git revert 42998ef08aba
  git revert ae626eb97376

Christoph, Robin, since you are the authors of these commits, do you
have any idea what could be happening? Are we able to fix this without
reverting those commits, before 6.0?

Marek