On Tue, Nov 12, 2013 at 03:42:59PM +0100, Martin Sperl wrote:

Not fully read this yet but one thing...

> >The messages and transfers ought to be totally reusable already, the
> >only bit that should need to be recreated is any data the driver creates
> >internally, most likely that's only going to be data for DMA.  We do
> >already have an interface for drivers to do the DMA mapping though it's
> >not very well loved at the minute...

> What DMA-interface are you talking about? at least in spi.h in 3.10
> I find nothing that would indicate an extra DMA interface...

Drivers can supply pre-mapped DMA buffers if they set is_dma_mapped
which is about as good as you get with dmaengine at the minute.  The
main opportunities for enhancement here are in the master interface
rather than the client, at least as things stand.