dynamic DMA-buf sharing between devices

[Christian König]

Hi everybody,

core idea in this patch set is that DMA-buf importers can now provide an optional invalidate callback. Using this callback and the reservation object exporters can now avoid pinning DMA-buf memory for a long time while sharing it between devices.

I've already send out an older version roughly a year ago, but didn't had time to further look into cleaning this up.

The last time a major problem was that we would had to fix up all drivers implementing DMA-buf at once.

Now I avoid this by allowing mappings to be cached in the DMA-buf attachment and so driver can optionally move over to the new interface one by one.

This is also a prerequisite to my patchset enabling sharing of device memory with DMA-buf.

Please review and/or comment,
Christian.