linux-kernel - Re: [PATCH 1/4 v2] dmaengine: add a tx_free method to struct dma_async_tx

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Date:	Wed, 10 Dec 2008 12:58:09 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Guennadi Liakhovetski" <g.liakhovetski@....de>
Cc:	linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net, adaplas@...il.com,
	"Sascha Hauer" <s.hauer@...gutronix.de>,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: [PATCH 1/4 v2] dmaengine: add a tx_free method to struct dma_async_tx_descriptor

On Wed, Dec 10, 2008 at 3:36 AM, Guennadi Liakhovetski
<g.liakhovetski@....de> wrote:
> From: Guennadi Liakhovetski <lg@...x.de>
>
> Some users reuse DMA transaction descriptors multiple times and need an
> explicit call to release them. An example of such a user is Video4Linux, which
> has to be able to release descriptors on ioctl(VIDIOC_DQBUF).
>
> Signed-off-by: Guennadi Liakhovetski <lg@...x.de>


Hi Guennadi,

Other dmaengine drivers have tasklets that scan the list of completed
descriptors and free the "acked" ones.  This happens in the cleanup
tasklet...
/me looks
...hmm this driver does not have a cleanup routine?  Ideally support
for ioctl(VIDIOC_DQBUF) could be achieved through this mechanism
without needing to increase the size of dma_async_tx_descriptor (which
has cache utilization impacts on other drivers).

--
Dan
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