Re: [PATCH 4/8] dma-buf: add peer2peer flag

[Christoph Hellwig <hch@infradead.org>]

On Fri, Apr 20, 2018 at 12:44:01PM +0200, Christian König wrote:
> > > What we need is an sg_alloc_table_from_resources(dev, resources,
> > > num_resources) which does the handling common to all drivers.
> > A structure that contains
> > 
> > {page,offset,len} + {dma_addr+dma_len}
> > 
> > is not a good container for storing
> > 
> > {virt addr, dma_addr, len}
> > 
> > no matter what interface you build arond it.
> 
> Why not? I mean at least for my use case we actually don't need the virtual
> address.

If you don't need the virtual address you need scatterlist even list.

> What we need is {dma_addr+dma_len} in a consistent interface which can come
> from both {page,offset,len} as well as {resource, len}.

Ok.

> What I actually don't need is separate handling for system memory and
> resources, but that would we get exactly when we don't use sg_table.

At the very lowest level they will need to be handled differently for
many architectures, the questions is at what point we'll do the
branching out.