Re: dmaengine/Query: What about scatter/gather for mem to mem transfers.

[Pratyush Anand]

On 1/2/2012 5:05 PM, Vinod Koul wrote:
> On Tue, 2011-12-20 at 15:45 +0530, Pratyush Anand wrote:
> > >  On 12/20/2011 2:51 PM, Vinod Koul wrote:
> > > >  >  On Thu, 2011-12-15 at 12:26 +0530, Pratyush Anand wrote:
> > > > > > >  >>>>  That way existing mechanism would work well for you.
> > > > > > >  >>>>  You need to split the chunks properly, which is what dma would do
> > > > >  >>  anyway
> > > > > > >  >>>>
> > > > > >  >>>
> > > > > >  >>>  Yes, they can be split like this, but then splitting onus will go on
> > > > >  >>  dma
> > > > > >  >>>  user driver, and so there would be replication of similar logic at
> > > > > >  >>>  several places. Therefore, I was thinking to make device_prep_dma_sg
> > > > >  >>  as
> > > > > >  >>>  generic by adding these flags.
> > > >  >  Well I am not sure how adding flags handles this?
> > >
> > >  device_prep_dma_sg has last argument as flags. dma user driver can pass
> > >  information about inc/dec of src/dst in this flag, which can be used by
> > >  the dma driver. I have put one such implementation at the end of mail.
> with the split pre-done would we need to do this, hence the referred
> implementation.

even with pre-done, some flag in this function will be needed. Because 
HW also need o know whether to src and dst are in incrementing or 
decrementing order.



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