RFC Resolve unwanted DMA backing with IOMMU

Hello,

There is a trouble on ARM with DMA allocations made by device drivers, the trouble is that DMA allocations are getting implicitly backed with IOMMU mapping by the driver core if IOMMU presents in a system and IOMMU could handle device. This is an undesired behaviour for drivers that manage IOMMU by themselves, like NVIDIA Tegra GPU driver. On arm32 the implicit backing happens if CONFIG_ARM_DMA_USE_IOMMU=y (multiplatform kernel configuration), on arm64 it happens if IOMMU domain type for a device is equal to IOMMU_DOMAIN_DMA.

The proposed solution adds a new option to the base device driver structure that allows device drivers to explicitly convey to the drivers core that the implicit IOMMU backing for devices must not happen.

Dmitry Osipenko (6):
driver core: Add option for disabling of backing devices DMA with
IOMMU
of/device: Don't back devices DMA with IOMMU if that's undesired by
driver
drm/tegra: Avoid implicit DMA backing with IOMMU
gpu: host1x: Avoid implicit DMA backing with IOMMU drm/nouveau: tegra: Universally avoid implicit DMA backing with IOMMU Revert "drm/nouveau: tegra: Detach from ARM DMA/IOMMU mapping"

 drivers/gpu/drm/nouveau/nouveau_platform.c         |  1 +
 drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c | 13 -------------
 drivers/gpu/drm/tegra/dc.c                         |  1 +
 drivers/gpu/drm/tegra/gr2d.c                       |  1 +
 drivers/gpu/drm/tegra/gr3d.c                       |  1 +
 drivers/gpu/drm/tegra/vic.c                        |  1 +
 drivers/gpu/host1x/dev.c                           |  1 +
 drivers/of/device.c                                |  7 +++++++
 include/linux/device.h                             |  2 ++
 9 files changed, 15 insertions(+), 13 deletions(-)

2.18.0