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

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Message-ID: <CACRpkdY-4wWeD=3mJiChi6+4=iBMcd3kVh3h4JmDZ5ySXY3KCA@mail.gmail.com>
Date:	Tue, 17 Jan 2012 09:52:15 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Viresh Kumar <viresh.kumar@...com>
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 Mon, Jan 16, 2012 at 12:44 PM, Viresh Kumar <viresh.kumar@...com> wrote:
> On 1/16/2012 4:24 PM, Russell King - ARM Linux wrote:
>> Note that DMA engine drivers are not responsible for unmapping the buffers
>> when the transfer completes - that is the responsibility of the caller.
>>
>> The automatic buffer unmapping is required for the async_tx APIs and
>> offload APIs.
>
> In dw_dmac, it is only done for slave transfers. Is this Okay ??

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.

Why do you want to do this?

Yours,
Linus Walleij
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