linux-kernel - RE: dmaengine/Query: What about scatter/gather for mem to mem transfers.

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Date:	Thu, 15 Dec 2011 05:06:56 +0000
From:	"Koul, Vinod" <vinod.koul@...el.com>
To:	Pratyush Anand <pratyush.anand@...com>,
	"Williams, Dan J" <dan.j.williams@...el.com>
CC:	Viresh KUMAR <viresh.kumar@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	Armando VISCONTI <armando.visconti@...com>,
	Deepak SIKRI <deepak.sikri@...com>,
	Vipin KUMAR <vipin.kumar@...com>,
	Vipul Kumar SAMAR <vipulkumar.samar@...com>,
	Vincenzo FRASCINO <Vincenzo.FRASCINO@...com>,
	Mirko GARDI <mirko.gardi@...com>,
	Rajeev KUMAR <rajeev-dlh.kumar@...com>,
	Amit VIRDI <Amit.VIRDI@...com>,
	Bhupesh SHARMA <bhupesh.sharma@...com>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>
Subject: RE: dmaengine/Query: What about scatter/gather for mem to mem
 transfers.

> 
> Hello Vinod/Dan,
> 
> Please write your opinion.
I am on vacation, but will reply briefly here, more next week
> 
> 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

--
~Vinod