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

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Message-ID: <4EE98478.5070209@st.com>
Date:	Thu, 15 Dec 2011 10:54:08 +0530
From:	Pratyush Anand <pratyush.anand@...com>
To:	"Koul, Vinod" <vinod.koul@...el.com>
Cc:	"Williams, Dan J" <dan.j.williams@...el.com>,
	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.

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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