iommu/arm-smmu: Move handing of RESUME to the context fault handler

iommu/arm-smmu: Move handing of RESUME to the context fault handler

The upper layer fault handler is now expected to handle everything
required to retry the transaction or dump state related to it, since we
enable threaded IRQs. This means that we can take charge of writing
RESUME, making sure that we always write it after writing FSR as
recommended by the specification.

The iommu handler should write -EAGAIN if a transaction needs to be
retried. This avoids tricky cross-tree changes in drm/msm, since it
never wants to retry the transaction and it already returns 0 from its
fault handler. Therefore it will continue to correctly terminate the
transaction without any changes required.

devcoredumps from drm/msm will temporarily be broken until it is fixed
to collect devcoredumps inside its fault handler, but fixing that first
would actually be worse because MMU-500 ignores writes to RESUME unless
all fields of FSR (except SS of course) are clear and raises an
interrupt when only SS is asserted. Right now, things happen to work
most of the time if we collect a devcoredump, because RESUME is written
asynchronously in the fault worker after the fault handler clears FSR
and finishes, although there will be some spurious faults, but if this
is changed before this commit fixes the FSR/RESUME write order then SS
will never be cleared, the interrupt will never be cleared, and the
whole system will hang every time a fault happens. It will therefore
help bisectability if this commit goes first.

I've changed the TBU path to also accept -EAGAIN and do the same thing,
while keeping the old -EBUSY behavior. Although the old path was broken
because you'd get a storm of interrupts due to returning IRQ_NONE that
would eventually result in the interrupt being disabled, and I think it
was dead code anyway, so it should eventually be deleted. Note that
drm/msm never uses TBU so this is untested.

Signed-off-by: Connor Abbott <cwabbott0@gmail.com>
Link: https://lore.kernel.org/r/20250520-msm-gpu-fault-fixes-next-v8-2-fce6ee218787@gmail.com
Signed-off-by: Will Deacon <will@kernel.org>