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

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Message-ID: <4F019A19.3060701@st.com>
Date:	Mon, 2 Jan 2012 17:20:49 +0530
From:	Pratyush Anand <pratyush.anand@...com>
To:	Vinod Koul <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 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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