videobuf-dma-contig.c cached user mapping

videobuf-dma-contig.c cached user mapping

[Matthieu CASTET]

Hi,

I would like to add support for cached user mapping to
videobuf-dma-contig.c.

For enabling this, "vma->vm_page_prot =
pgprot_noncached(vma->vm_page_prot);" line should be removed.

But now we should ensure user mapping cache coherency.
For that, 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 ?


Thanks,
Matthieu