linux-kernel - Re: [RFC v2 0/5] dmaengine: Slave DMA interface and example users

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Message-Id: <200801292256.14553.david-b@pacbell.net>
Date:	Tue, 29 Jan 2008 22:56:14 -0800
From:	David Brownell <david-b@...bell.net>
To:	Haavard Skinnemoen <hskinnemoen@...el.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org,
	Shannon Nelson <shannon.nelson@...el.com>,
	kernel@...32linux.org, "Francis Moreau" <francis.moro@...il.com>,
	"Paul Mundt" <lethal@...ux-sh.org>,
	"Vladimir A. Barinov" <vbarinov@...mvista.com>,
	Pierre Ossman <drzeus-list@...eus.cx>
Subject: Re: [RFC v2 0/5] dmaengine: Slave DMA interface and example users

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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