Re: [RFC v3 4/7] dmaengine: Add slave DMA interface

[Haavard Skinnemoen <hskinnemoen@atmel.com>]

On Wed, 13 Feb 2008 12:07:26 -0700
"Dan Williams" <dan.j.williams@intel.com> wrote:

> > +struct dma_slave_descriptor {
> > +       struct dma_async_tx_descriptor txd;
> > +       struct list_head client_node;
> > +};  
> 
> Can you explain a bit why client_node is needed?  I do not think we
> need dma_slave_descriptor if dma_unmap data / control is added to
> dma_async_tx_descriptor.  Hmm?

Well, it's perhaps not needed for slave transfers as such. But the MMC
driver (and I suspect quite a few other users of the slave interface)
deals with scatterlists, so it needs a way to keep track of all the
descriptors it submits. Hence the list node.

But looking at your latest patch series, I guess we can use the new
"next" field instead. It's not like we really need the full
capabilities of list_head.

Haavard