[RFC] iommu: arm-smmu: stall support

On Tue, Sep 19, 2017 at 10:23:43AM -0400, Rob Clark wrote:

I would like to decide in the IRQ whether or not to queue work or not,
because when we get a gpu fault, we tend to get 1000's of gpu faults
all at once (and I really only need to handle the first one).  I
suppose that could also be achieved by having a special return value
from the fault handler to say "call me again from a wq"..

Note that in the drm driver I already have a suitable wq to queue the
work, so it really doesn't buy me anything to have the iommu driver
toss things off to a wq for me.  Might be a different situation for
other drivers (but I guess mostly other drivers are using iommu API
indirectly via dma-mapping?)

Okay, so since you are the only user for now, we don't need a
work-queue. But I still want the ->resume call-back to be hidden in the
iommu code and not be exposed to users.

We already have per-domain fault-handlers, so the best solution for now
is to call ->resume from report_iommu_fault() when the fault-handler
returns a special value.


Regards,

	Joerg