linux-kernel - Re: [PATCH 16/18] dmaengine/ambhe rest oa-pl08x: Add support for sg len greater than one for slave transfers

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Message-ID: <1315518873.6638.7.camel@vkoul-mobl4>
Date:	Fri, 09 Sep 2011 03:24:33 +0530
From:	Vinod Koul <vkoul@...radead.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	vinod.koul@...el.com, Viresh Kumar <viresh.kumar@...com>,
	Pratyush ANAND <pratyush.anand@...com>,
	Rajeev KUMAR <rajeev-dlh.kumar@...com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	Bhupesh SHARMA <bhupesh.sharma@...com>,
	Armando VISCONTI <armando.visconti@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vipin KUMAR <vipin.kumar@...com>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	Amit VIRDI <Amit.VIRDI@...com>,
	Vipul Kumar SAMAR <vipulkumar.samar@...com>,
	"viresh.linux@...il.com" <viresh.linux@...il.com>,
	Deepak SIKRI <deepak.sikri@...com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 16/18] dmaengine/ambhe rest oa-pl08x: Add support for
 sg len greater than one for slave transfers

On Thu, 2011-09-08 at 12:29 +0200, Linus Walleij wrote:
> On Thu, Sep 8, 2011 at 5:50 AM, Viresh Kumar <viresh.kumar@...com> wrote:
> 
> > If i am getting this clearly, the concern is "why to queue separate transfers for
> > individual sg's? Better would be to prepare the complete list at once and
> > start the transfer, so that DMA stops only after finishing all sg's
> > passed from user." Is this what you are pointing at?
> 
> Yes.
> 
> > If yes, then the same is done in this patch too. An array for llis is allocated at
> > the start, then for each sg i prepare lli list from this array. Last lli from one sg
> > is followed by first lli from next sg. And so i get a continuous chain of llis.
> 
> OK so I guess I was lost in the code ...
> 
> So this is mainy cached as txd->dsg_list so you can quickly retrieve the
> number of bytes pending in the LLI by traversing that sglist.
> 
> This is better than what the coh901318 does, because that driver
> resorts to going into the physical LLIs themselves to retrieve this
> info.
> 
> It also seems like this will play nice with Per Forlin's MMC
> speed-up patches, so that will become effective for your MMC
> usecases.
> 
> Now I really like this patch.
> 
> Sorry for being such a slow learner!
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
Okay, great. I will check the rest of the series (i think 3 patches) and
apply then next week.

-- 
~Vinod Koul
Intel Corp.

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