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
