[Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism

[Alan Cox]

> I still don't think that's possible. Please explain how you expect
> to change the semantics of the streaming mapping API to allow multiple
> mappers without having explicit serialization points that are visible
> to all users. For simplicity, let's assume a cache coherent system

I would agree. It's not just about barriers but in many cases where you
have multiple mappings by hardware devices the actual hardware interface
is specific to the devices. Just take a look at the fencing in TTM and
the graphics drivers.

Its not something the low level API can deal with, it requires high level
knowledge.

Alan