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SubjectRe: [RFC PATCH 1/2] RapidIO: Add DMA Engine support for RIO data transfers
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On Mon, 2011-10-17 at 21:22 +0530, Jassi Brar wrote:
> On 15 October 2011 23:05, Vinod Koul <vinod.koul@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.
Yes agreed, but we already decided and marked it as depreciated.

> And then either this argument would be RapidIO specific (unfair
> to other users) or generic. In latter case what would it look like ?
My initial thoughts were to add an argument which only the specific dmac
knows howto decode and is filled by its client. As i said for existing
users and people who don't require dynamic information wouldn't bother.
The pros
- allows us to support RIO kind of subsystems where one needs to pass
subsystem specific information for programing the dmac
- doesn't require us to add subsystem specific stuff in dmaengine,
today its RIO tomorrow some other folks may want to add. We want to
maintain dmaengine as a generic framework, while also trying to support
multiple audiences.
Cons:
- there is no guarantee; dmac expects foo and clients pass bar

I am okay if we have alternate way to support this with above goal :)

--
~Vinod



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