videobuf cached user mapping

Hi,

Is that possible to have user mapping cached in Memory Mapping mode ?

This means buffer allocated by mmap in userspace, will have cache support, and it will be faster to work on it.

But how the cache coherency can be done ?

For a camera we should :
- invalidate cache before dma operation (to have not old buffer data in the cache)
- forbid the user to access the buffer during the dma operation (to not pollute the cache)

Is it possible ?
How can we achieve that ?

I see sync method, that seems only called after frame capture ?

Or user "User Pointers" is the solution ?
But they should have the same problems. Is there some documentation of how "user pointer" are synchronised with dma ?

Thanks,
Matthieu