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: <1316499574.31295.3.camel@vkoul-udesk3>
Date:	Tue, 20 Sep 2011 11:49:34 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	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 Fri, 2011-09-09 at 03:24 +0530, Vinod Koul wrote:
> 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.
Applied the remaining two patches for the series to my next

-- 
~Vinod

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