linux-kernel - Re: [PATCH 7/8] dmaengine/dw_dmac: Unmap all memory buffers after completion of slave transfers

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Message-ID: <4F153A3E.8010409@st.com>
Date:	Tue, 17 Jan 2012 14:37:10 +0530
From:	Viresh Kumar <viresh.kumar@...com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	Pratyush ANAND <pratyush.anand@...com>,
	Rajeev KUMAR <rajeev-dlh.kumar@...com>,
	Bhupesh SHARMA <bhupesh.sharma@...com>,
	Armando VISCONTI <armando.visconti@...com>,
	Mirko GARDI <mirko.gardi@...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>,
	Bhavna YADAV <bhavna.yadav@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Vincenzo FRASCINO <Vincenzo.FRASCINO@...com>
Subject: Re: [PATCH 7/8] dmaengine/dw_dmac: Unmap all memory buffers after
 completion of slave transfers

On 1/17/2012 2:22 PM, Linus Walleij wrote:
> Basically the driver using the dmaengine shall map/unmap buffers
> used for slave transfers, not the driver.
> 
> I usually map them before setting up a transfer and unmaps them
> when egtting the callback from the DMA engine that the transfer is
> complete.
> 

You implemented similar stuff in amba-pl08x :) .

if (!plchan->slave)
	pl08x_unmap_buffers(txd);

> Why do you want to do this?

This is because people can pass in flags which are
DMA_COMPL_SKIP_SRC_UNMAP, etc.

If they are not passed, then DMA driver must do it for them.

Sorry if i am understanding the DMA logic incorrectly.

-- 
viresh
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