[RFC PATCH 1/2] RapidIO: Add DMA Engine support for RIO data transfers

[Bounine, Alexandre]

On Mon, Oct 17, 2011 at 11:53 AM, Jassi Brar
<jaswinder.singh at linaro.org> wrote:
> 
> On 15 October 2011 23:05, Vinod Koul <vinod.koul at intel.com> wrote:
> 
> > Another alternate approach could be to add one more argument to
> > prep_slave_sg API which allows us to pass additional runtime
specific
> > parameters. This can be NULL and unused for existing drivers and
used
> in
> > RIO and any future subsystems which want to use dmaengine.
> > Thoughts...?
> >
> That doesn't sound much different than passing the data via
> dma_chan.private during prep_slave_sg. Only now we add to
> the number of arguments.
One dma_chan may be used by multiple drivers requesting data transfer.
In this case we will need a lock to keep dma_chan and its private
coupled together. 
If we consider this coupling as a valid way we may think about
adding a lock member into dma_chan structure. This will make locking
more effective for configurations with multiple DMA channels. 

> And then either this argument would be RapidIO specific (unfair
> to other users) or generic. In latter case what would it look like ?
It should not be RapidIO specific. Just transfer specific context that
will be interpreted by participants. Given that we have a channel
filtering mechanism there is a little chance of wrongful usage of
that parameter.

Alex.