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

Rob Clark
2019-07-03T01:50:22Z

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(-)

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2.20.1