# Re: \[RFC V2\] virtio: Add platform specific DMA API translation for virito devices

- From: Christoph Hellwig \<hch@infradead.org\>
- Date: 2018-06-15 09:16:35 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2018/06/5308569
- Thread: https://ratatoskr.run/linuxppc-dev/2018/05/5289219/t.md

```text
On Wed, Jun 13, 2018 at 11:11:01PM +1000, Benjamin Herrenschmidt wrote:
> Actually ... the stuff in lib/dma-direct.c seems to be just it, no ?
> 
> There's no cache flushing and there's no architecture hooks that I can
> see other than the AMD security stuff which is probably fine.
> 
> Or am I missing something ?

You are missing the __phys_to_dma arch hook that allows architectures
to adjust the dma address.  Various systems have offsets, or even
multiple banks with different offsets there.  Most of them don't
use the dma-direct code yet (working on it), but there are a few
examples in the tree already.
```