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

[Pratyush Anand]

On 12/15/2011 10:36 AM, Koul, Vinod wrote:
> > Hello Vinod/Dan,
> >
> > Please write your opinion.
> I am on vacation, but will reply briefly here, more next week

Thanks for your quick reply.

> > Regards
> > Pratyush
> >
> > On 12/14/2011 12:17 PM, Pratyush Anand wrote:
> > > Hello Vinod/Dan,
> > >
> > > In continuation to the scatter/gather requirement:
> > > We might need some generic transfer where source and destination
> > > address may be overlapped and also gap between two chunk of source and
> > > destination might not be same.
> > >
> > > For examaple,
> > > Transfer size is - -0x4000
> > > Our Src is something like this:
> > > 0x1000 -- 0x2000
> > > 0x3000 -- 0x5000
> > > 0x6000 -- 0x7000
> > >
> > > and dst is something like this:
> > > 0x6000 -- 0x8000
> > > 0x9000 -- 0xB000
> So why can't it be split like:
> 0x1000--0x2000 =>  0x6000 --0x7000
> 0x3000 -- 0x4000 =>  0x7000 - 0x8000
> 0x4000 -- 0x5000 =>  0x9000 - 0xA000
> 0x6000 -- 0x7000 =>  0xA000 - 0xB000
>
> 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.

Regards
Pratyush

> --
> ~Vinod

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