[PATCH 1/5] dma-buf: add optional invalidate_mappings callback v2

[Chris Wilson]

Quoting Christian König (2018-03-16 14:22:32)
[snip, probably lost too must context]
> This allows for full grown pipelining, e.g. the exporter can say I need 
> to move the buffer for some operation. Then let the move operation wait 
> for all existing fences in the reservation object and install the fence 
> of the move operation as exclusive fence.

Ok, the situation I have in mind is the non-pipelined case: revoking
dma-buf for mmu_invalidate_range or shrink_slab. I would need a
completion event that can be waited on the cpu for all the invalidate
callbacks. (Essentially an atomic_t counter plus struct completion; a
lighter version of dma_fence, I wonder where I've seen that before ;)

Even so, it basically means passing a fence object down to the async
callbacks for them to signal when they are complete. Just to handle the
non-pipelined version. :|
-Chris