[PATCH v3 0/2] iommu: handle drivers that manage iommu directly

[Rob Clark]

From: Rob Clark <robdclark@xxxxxxxxxxxx>

One of the challenges we have to enable the aarch64 laptops upstream
is dealing with the fact that the bootloader enables the display and
takes the corresponding SMMU context-bank out of BYPASS.  Unfortunately,
currently, the IOMMU framework attaches a DMA (or potentially an
IDENTITY) domain before the driver is probed and has a chance to
intervene and shutdown scanout.  Which makes things go horribly wrong.

But in this case, drm/msm is already directly managing it's IOMMUs
directly, the DMA API attached iommu_domain simply gets in the way.
This series adds a way that a driver can indicate to drivers/iommu
that it does not wish to have an DMA managed iommu_domain attached.
This way, drm/msm can shut down scanout cleanly before attaching it's
own iommu_domain.

NOTE that to get things working with arm-smmu on the aarch64 laptops,
you also need a patchset[1] from Bjorn Andersson to inherit SMMU config
at boot, when it is already enabled.

[1] https://www.spinics.net/lists/arm-kernel/msg732246.html

NOTE that in discussion of previous revisions, RMRR came up.  This is
not really a replacement for RMRR (nor does RMRR really provide any
more information than we already get from EFI GOP, or DT in the
simplefb case).  I also don't see how RMRR could help w/ SMMU handover
of CB/SMR config (Bjorn's patchset[1]) without defining new tables.

This perhaps doesn't solve the more general case of bootloader enabled
display for drivers that actually want to use DMA API managed IOMMU.
But it does also happen to avoid a related problem with GPU, caused by
the DMA domain claiming the context bank that the GPU firmware expects
to use.  And it avoids spurious TLB invalidation coming from the unused
DMA domain.  So IMHO this is a useful and necessary change.

Rob Clark (2):
  iommu: add support for drivers that manage iommu explicitly
  drm/msm: mark devices where iommu is managed by driver

 drivers/gpu/drm/msm/adreno/adreno_device.c | 1 +
 drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c    | 1 +
 drivers/gpu/drm/msm/disp/mdp5/mdp5_kms.c   | 1 +
 drivers/gpu/drm/msm/msm_drv.c              | 1 +
 drivers/iommu/iommu.c                      | 2 +-
 drivers/iommu/of_iommu.c                   | 3 +++
 include/linux/device.h                     | 3 ++-
 7 files changed, 10 insertions(+), 2 deletions(-)

-- 
2.21.0