From: Rob Clark robdclark@chromium.org
One of the challenges we need to handle 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[1] scanout. Which makes things go horribly wrong.
This also happens to solve a problem that is blocking us from supporting per-context pagetables on the GPU, due to domain that is attached before driver has a chance to attach it's own domain for the GPU.
But since the driver is managing it's own iommu domains directly, and does not use dev->iommu_group->default_domain at all, the simple solution to both problems is to just avoid attaching that domain in the first place.
[1] Eventually we want to be able to do a seemless transition from efifb to drm/msm... but first step is to get the core (iommu, clk, genpd) pieces in place, so a first step of disabling the display before first modeset enables us to get all of the dependencies outside of drm/msm in place. And this at least gets us parity with windows (which also appears to do a modeset between bootloader and HLSO). After that there is a bunch of drm/msm work that is probably not interesting to folks outside of dri-devel.
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 | 11 +++++++++++ include/linux/device.h | 3 ++- 6 files changed, 17 insertions(+), 1 deletion(-)