linux-kernel - Re: [PATCH] DMA: Correct invalid assumptions in the Kconfig text

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Date:	Wed, 24 Oct 2007 08:55:58 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Haavard Skinnemoen" <hskinnemoen@...el.com>
Cc:	"Shannon Nelson" <shannon.nelson@...el.com>,
	linux-kernel@...r.kernel.org,
	"David Brownell" <david-b@...bell.net>, kernel@...32linux.org,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: [PATCH] DMA: Correct invalid assumptions in the Kconfig text

Hi Haavard,

On 10/24/07, Haavard Skinnemoen <hskinnemoen@...el.com> wrote:
> This patch corrects what I hope are invalid assumptions about the DMA
> engine layer: Not only Intel(R) hardware can do DMA, and DMA can be
> used for other things than memcpy and RAID offloading.
>
> At the same time, make the DMA Engine menu visible again on AVR32. I'm
> currently working on a driver for a DMA controller that can do
> mem-to-mem transfers (which is supported by the framework) as well as
> device-to-mem and mem-to-device transfers (not currently supported.)
>
> Signed-off-by: Haavard Skinnemoen <hskinnemoen@...el.com>
> ---
> Don't get me wrong; I think Intel deserves lots of respect for
> creating this framework. But this is also why I got a bit disappointed
> when I discovered that it seems to be less generic than I initially
> hoped.
>

Patches welcome :-)

> DMA controllers, which may support plain memcpy acceleration in
> addition to more traditional "slave DMA", are very common in SoC
> devices, and I think Linux needs a common framework for it. The
> existing DMA Engine framework seems to come pretty close already, but
> I think it needs more input from the embedded crowd before it can be
> completely usable on a large number of embedded systems.
>

Part of the problem of supporting slave/device DMA along side generic
memcpy/xor/memset acceleration is that it adds a number of caveats and
restrictions to the interface.  One idea is to create another client
layer, similar to async_tx, that can handle the architecture specific
address, bus, and device pairing restrictions.  In other words make
device-dma a superset of the generic offload capabilities and move it
to its own channel management layer.

> I'm not going to suggest any changes to the actual framework for
> 2.6.24, but I think the _intention_ of the framework needs to be
> clarified.
>

Should this patch wait until the framework has been extended?

Otherwise, Acked-by: Dan Williams <dan.j.williams@...el.com>

> Haavard
>

Regards,
Dan
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