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From: David Brownell <david-b@pacbell.net>
To: Haavard Skinnemoen <hskinnemoen@atmel.com>
Subject: Re: [RFC v2 0/5] dmaengine: Slave DMA interface and example users
Date: Tue, 29 Jan 2008 22:56:14 -0800
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Cc: Dan Williams <dan.j.williams@intel.com>, linux-kernel@vger.kernel.org,
       Shannon Nelson <shannon.nelson@intel.com>, kernel@avr32linux.org,
       "Francis Moreau" <francis.moro@gmail.com>,
       "Paul Mundt" <lethal@linux-sh.org>,
       "Vladimir A. Barinov" <vbarinov@ru.mvista.com>,
       Pierre Ossman <drzeus-list@drzeus.cx>
References: <1201630213-31900-1-git-send-email-hskinnemoen@atmel.com> <20080129215453.1e3758ab@siona>
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On Tuesday 29 January 2008, Haavard Skinnemoen wrote:
>
> Btw, there's one issue I forgot to mention: I believe the DMA Engine
> framework is currently misusing the DMA mapping API, and this patchset
> makes things worse.
> 
> Currently, the async_tx bits of the API do the required calls to
> dma_map_single() and/or dma_map_page(), but they rely on the driver to
> do the unmapping. This is problematic ...
> 
> How do we solve this?

How about:  for peripheral DMA, don't let the engine see anything
except dma_addr_t values.

The engine needs to be able to dma_alloc_coherent() memory too,
which is pre-mapped.

- Dave
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